Parenting - Cognitive Classes and Social Behavior - The Bell Curve: Intelligence and Class Structure in American Life - Richard J. Herrnstein, Charles Murray

The Bell Curve: Intelligence and Class Structure in American Life - Richard J. Herrnstein, Charles Murray (1996)

Part II. Cognitive Classes and Social Behavior

Chapter 10. Parenting

Everyone agrees, in the abstract and at the extremes, that there is good parenting and poor parenting. This chapter addresses the uncomfortable question: Is the competence of parents at all affected by how intelligent they are?

It has been known for some time that socioeconomic class and parenting are linked, both to disciplinary practices and to the many ways in which the intellectual and emotional development of the child are fostered. On both counts, parents with higher socioeconomic status look better. At the other end of the parenting continuum, neglect and abuse are heavily concentrated in the lower socioeconomic classes.

Whenever an IQ measure has been introduced into studies of parent-child relationships, it has explained away much of the differences that otherwise would have been attributed to education or social class, but the examples are sparse. The NLSY provides an opportunity to fill in a few of the gaps.

With regard to prenatal and infant care, low IQ among the white mothers in the NLSY sample was related to low birth weight, even after controlling for socioeconomic background, poverty, and age of the mother. In the NLSY’s surveys of the home environment, mothers in the top cognitive classes provided, on average, better environments for children than the mothers in the bottom cognitive classes. Socioeconomic background and current poverty also played significant roles, depending on the specific type of measure and the age of the children.

In the NLSY’s measures of child development, low maternal IQ was associated with problematic temperament in the baby and with low scores on an index of “friendliness,” with poor motor and social development of toddlers and with behavioral problems from age 4 on up. Poverty usually had a modest independent role but did not usually diminish the contribution of IQ (which was usually also modest). Predictably, the mothers IQ was also strongly related to the IQ of the child.

Taking these data together, the NLSY results say clearly that high IQ is by no means a prerequisite for being a good mother. The disquieting finding is that the worst environments for raising children, of the kind that not even the most resilient children can easily overcome, are concentrated in the homes in which the mothers are at the low end of the intelligence distribution.

Parenting, in one sense the most private of behaviors, is in another the most public. Parents make a difference in the way their children turn out—whether they become law abiding or criminal, generous or stingy, productive or dependent. How well parents raise their children has much to do with how well the society functions.

But how are parents to know whether they are doing a good or a bad job as parents? The results seem to be hopelessly unpredictable. Most people know at least one couple who seem to be the ideal parents but whose teenage child ends up on drugs. Parents with more than one child are bemused by how differently their children respond to the same home and parental style. And what makes a good parent anyway? Most people also have friends who seem to be raising their children all wrong, and yet the children flourish.

The exceptions notwithstanding, the apparent unpredictability of parenting is another of those illusions fostered by the ground-level view of life as we live it from day to day. Parenting is more predictable in the aggregate than in the particular. The differences in parenting style that you observe among your friends are usually minor—the “restriction of range” problem that we discussed in Chapter 3. A middle-class mother may think that one of her friends is far too permissive or strict, but put against the full range of variation that police and social workers are forced to deal with, where “permissiveness” is converted into the number of days that small children are left on their own and “strictness” may be calibrated by the number of stitches required to close the wounds from a parental beating, the differences between her and her friend are probably small.

Despite all the differences among children and parents, there is such a thing as good parenting as opposed to bad—not precisely defined but generally understood. Our discussion proceeds from the assumption that good parenting includes (though is not restricted to) seeing to nourishment and health, keeping safe from harm, feeling and expressing love, talking with and listening to, helping to explore the world, imparting values, and providing a framework of rules enforced consistently but not inflexibly. Parents who more or less manage to do all those things, weassert, are better parents than people who do not. The touchy question of this chapter is: Does cognitive ability play any role in this? Are people with high IQs generally better parents than people with low IQs?


The relationship of IQ to parenting is another of those issues that social scientists have been slow to investigate. Furthermore, this is a topic for which the NLSY is limited. For unemployment, school dropout, illegitimacy, or welfare recipiency, the NLSY permits us to cut directly to the question, What does cognitive ability have to do with this behavior? But many of the NLSY indicators about parenting give only indirect evidence. To interpret that evidence, it is useful to begin with the large body of studies that have investigated whether social class affects parenting. Having described that relationship (which by now is reasonably well understood), we will be on firmer ground in drawing inferences about cognitive ability.

The first scholarly study of parenting styles among parents of different social classes dates back to 1936 and a White House conference on children.1 Ever since, the anthropologists and sociologists have told similar stories. Working-class parents tend to be more authoritarian than middle-class parents. Working-class parents tend to use physical punishment and direct commands, whereas middle-class parents tend to use reasoning and appeals to more abstract principles of behavior. The consistency of these findings extends from the earliest studies to the most recent.2

In an influential article published in 1959, Melvin Kohn proposed that the underlying difference was that working-class parents were most concerned about qualities in their children that ensure respectability, whereas middle-class parents were most concerned about internalized standards of conduct.3 Kohn argued that the real difference in the use of physical punishment was not that working-class parents punish more but that they punish differently from middle-class parents. Immediate irritants like boisterous play might evoke a whack from working-class parents, whereas middle-class parents tended to punish when the intent of the child’s behavior (knowingly hurting another child, for example) was problematic.4 Kohn concluded that “the working-class orientation … places few restraints on the impulse to punish the child when his behavior is out of bounds. Instead, it provides a positive rationale for punishing the child in precisely those circumstances when one might most like to do so.”5 To put it more plainly, Kohn found that working-class parents were more likely to use physical punishment impulsively, when the parents themselves needed the relief, not when it was likely to do the child the most good.

The middle-class way sounds like “better” behavior on the part of parents, not just a neutral socioeconomic difference in parenting style, and this raises a point that scholars on child development bend over backward to avoid saying explicitly: Generally, and keeping in mind the many exceptions, the conclusion to be drawn from the literature on parenting is that middle-class people are in fact better parents, on average, than working-class people. Readers who bridle at this suggestion are invited to reread the Kohn quotation above and ask themselves whether they can avoid making a value judgment about it.

Parenting differences among the social classes are not restricted to matters of discipline. Other major differences show up in the intellectual development of the child. Anthropologist Shirley Brice Heath6 gives vivid examples in her description of parenting in “Roadville,” a white lower-class community in the Carolinas, versus “Gateway,” a nearby community of white middle-class parents.7 The parents of Roadville were just as devoted to their children as the parents of Gateway. Roadville newborns came home to nurseries complete with the same mobiles, pictures, and books that the Gateway babies had. From an early age, Roadville children were held on laps and read to, talked to, and otherwise made as much the center of attention as Gateway babies. But the interactions differed, Heath found. Take bedtime stories, for example. In middle-class Gateway, the mother or father encouraged the children to ask questions and talk about what the stories meant, pointing at items on the page and asking what they were. The middle-class parents praised right answers and explained what was wrong with wrong ones.8 It is no great stretch to argue, as Robert Sternberg and others do, that this interaction amounts to excellent training for intelligence tests. Lower-class Roadville parents did not do nearly as much of that kind of explaining and asking.9 When the children were learning to do new tasks, the Roadville parents did not explain the “how” of things the way the Gateway parents did. Instead, the Roadville parents were more likely to issue directives (“Don’t twist the cookie cutter”) and hardly ever gave reasons for their instructions (“If you twist the cutter, the cookies will be rough on the edge”).10

When they got to school, the Roadville and Gateway children continued to differ. The working-class Roadville children performed well in the early tasks of each of the first three grades. They knew the alphabet when they went to kindergarten; they knew how to sit still in class and could perform well in the reading exercises that asked them to identify specific portions of words or to link two items on the same page of the book. But if the teacher asked, “What did you like about the story?” or “What would you have done if you had been the child in that story?” the Roadville children were likely to say “I don’t know” or shrug their shoulders, while the middle-class Gateway children would more often respond easily and imaginatively.11

Heath’s conclusions drawn from her anthropological observations are buttressed by the quantitative work that has been done to date. A review of the technical literature in the mid-1980s put it bluntly: “It is an empirical fact that children from relatively higher SES families receive an intellectually more advantageous home environment. This finding holds for white, black, and Hispanic children, for children within lower- and middle-SES families, as well as for children born preterm and full-term.”12


To this point, we have been talking about parenting within the normal range. Now we turn to child neglect and child abuse, increasingly labeled “malparenting” in the technical literature.

Abuse and neglect are distinct. The physical battering and other forms of extreme physical and emotional punishment that constitute child abuse get most of the publicity, but child neglect is far more common, by ratios ranging from three to one to ten to one, depending on the study.13 Among the distinctions that the experts draw between child abuse and neglect are these:

Abuse is an act of commission, while neglect is more commonly an act of omission.

Abuse is typically episodic and of short duration; neglect is chronic and continual.

Abuse typically arises from impulsive outbursts of aggression and anger; neglect arises from indifference, inattentiveness, or being overwhelmed by parenthood.14

Commonly, neglect is as simple as failure to provide a child with adequate food, clothing, shelter, or hygiene. But it can also mean leaving dangerous materials within reach, not keeping the child away from an open window, or leaving toddlers alone for hours at a time. It means not taking the child to a doctor when he is sick or not giving him the medicine the doctor prescribed. Neglect can also mean more subtle deprivations: habitually leaving babies in cribs for long periods, never talking to infants and toddlers except to scold or demand, no smiles, no bedtime stories. At its most serious, neglect becomes abandonment.

Are abusing parents also neglectful? Are neglectful parents also abusive? Different studies have produced different answers. Child abuse in some bizarre forms has nothing to do with anything except a profoundly deranged parent. Such cases crop up unpredictably, independent of demographic and socioeconomic variables.15

Once we move away from these exceptional cases, however, abuse and neglect seem to be more alike than different in their origins.16 The theories explaining them are complex, involving stress, social isolation, personality characteristics, community characteristics, and transmission of malparenting from one generation to the next.17 But one concomitant of malparenting is not in much dispute: Malparenting of either sort is heavily concentrated in the lower socioeconomic classes. Indeed, the link is such that, as Douglas Besharov has pointed out, behaviors that are sometimes classified as forms of neglect—letting a child skip school, for example—are not considered neglectful in some poor communities but part of the normal pattern of upbringing.18 What would be considered just an overenthusiastic spanking in one neighborhood might be called abuse in another.

We realize that once again we are contradicting what everyone knows, which is that “child abuse and neglect afflict all communities, regardless of race, religion, or economic status,” to pick one formulation of this common belief.19 And in a narrow technical sense, such statements are correct, insofar as neglect and abuse are found at every social and economic level, as is every other human behavior. It is also correct that only a small minority of parents among the poor and disadvantaged neglect or abuse their children. But the way such statements are usually treated in the media, by politicians, and by child advocacy groups is to imply that child neglect and abuse are spread evenly across social classes, as if children have about an equal chance of being abused or neglected whether they come from a rich home or a poor one, whether the mother is a college graduate or a high school dropout. And yet from the earliest studies to the present, malparenting has been strongly associated with socioeconomic class.

The people who argue otherwise do not offer data to make their case. Instead, they argue that child neglect and abuse are reported when it happens to poor children but not rich ones. Affluent families are believed to escape the reporting net (by using private physicians, for example, who are less likely to report abuse). Social service agencies are said to be reluctant to intervene in affluent families.20 Poor people are likely to be labeled deviant for behaviors that would go unnoted or unremarked in richer neighborhoods.21 People are likely to think the worst of socially unattractive people and give socially attractive people the benefit of the doubt.22

Studies spread over the last twenty years have analyzed reporting bias in a variety of ways, including surveys to identify abuse that goes unreported through official channels. The results are consistent: The socioeconomic link with maltreatment is authentic.23 Probably the link is stronger for neglect than for abuse.24 But specifying exactly how strongly socioeconomic status and child maltreatment are linked is difficult because of the genuine shortcomings of official reports and because so many different kinds of abuse and neglect are involved. The following numbers give a sense of the situation:

In an early national study (using data for 1967) 60 percent of the families involved in abuse incidents had been on welfare during or prior to the study year.25

In data on 20,000 validated reports of child abuse and neglect collected by the American Humane Association for 1976, half of the reported families were below the poverty line and most of the rest were concentrated just above it.26

In a 1984 study of child maltreatment in El Paso, Texas, 87 percent of the alleged perpetrators were in families with incomes under $18,000, roughly the bottom third of income. Seventy-three percent of the alleged female perpetrators were unmarried.27

In the federally sponsored National Incidence Study in 1979, which obtained information on unreported as well as reported cases, the families of 43 percent of the victims of child abuse or neglect had an income under $7,000, compared to 17 percent of all American children. Only 6 percent of the abusive or neglectful families had incomes of $25,000 or more.

The 1986 replication of the National Incidence Study found that the rate of abuse and neglect among families with incomes under $15,000 was five times that of families with incomes above $15,000. Only 6 percent of the families involved in neglect or abuse had incomes above the median for all American families.28

Other Precursors of Maltreatment

Premature births, low birth weight, and illegitimacy also have links with maltreatment. Studies in America and Britain have found rates of low birth weight among abused children running at three to four times the national average.29 Prematurity has been found to be similarly disproportionate among abused children.30 The proportion of neglected children who are illegitimate has run far above national averages in studies from the early 1960s onward. More than a quarter of the neglected children in the mid-1960s were illegitimate, for example—almost four times the national proportion.31 In a British sample, 36 percent of the neglected children were illegitimate compared to 6 percent in the control group.32

Given the one-sided nature of the evidence, why has the “myth of classlessness,” in Leroy Pelton’s phrase, been so tenacious? Pelton himself blamed social service professionals and politicians, arguing that both of these powerful groups have a vested interest in a medical model of child abuse, in which child abuse falls on its victims at random, like the flu.33 Pelton does not mention another reason that seems plausible to us: Child abuse and neglect are held in intense distaste by most Americans, who feel great hostility toward parents who harm their children. People who write about malparenting do not want to encourage this hostility to spill over into hostility toward the poor and disadvantaged.

Whatever the reasons, the myth of classlessness is alive and well. It is a safe bet that at the next Senate hearing on a child neglect bill, witnesses and senators alike will agree that neglect and abuse are scattered throughout society, and the next feature story on child neglect you see on the evening news will report, as scientific fact, that child neglect is not a special problem of the poor.


In all of these studies of socioeconomic status and parenting, the obvious but usually ignored possibility has been that the parents’ cognitive ability, not their status, was an important source of the differences in parenting styles and also an important source of the relationship between malparenting and children’s IQs. Indeed, even without conducting any additional studies, some sort of role for cognitive ability must be presupposed. If cognitive ability is a cause of socioeconomic status (yes) and if socioeconomic status is related to parenting style (yes), then cognitive ability must have at least some indirect role in parenting style. The same causal chain applies to child maltreatment.

Direct evidence for a link with IQ is sparse. Even the educational attainment of the abusing parents is often unreported. But a search of the literature through the early 1990s uncovered a number of fragments that point to a potentially important role for cognitive ability, if we bear in mind that cognitive ability is a stronger predictor of school dropout than is socioeconomic status (Chapter 6):

In Gil’s national study of child abuse reports, more than 65 percent of the mothers and 56 percent of the fathers had not completed high school.34

A study of 480 infants of women registering for prenatal care at an urban hospital for indigent persons and their children found that the less educated mothers even within this disadvantaged population were more likely to neglect their babies.35

Three studies of child maltreatment in a central Virginia city of 80,000 people found that neglecting families had an average eighth-grade education, and almost three-quarters of them had been placed in classes for the mentally retarded during their school years. In contrast with the neglecting families, the abusing families tended to be literate, high school graduates, and of normal intelligence.36

A study of fifty-eight preschool children of unspecified race in the Cleveland area with histories of failure to thrive found that their mothers’ IQs average was 81.37 No comparison group was available in this study, but a mean of 81 indicates cognitive functioning at approximately the 10th centile.

A study of twenty abusive or neglectful mothers and ten comparison mothers from inner-city Rochester, New York, found that maltreating and nonmaltreating mothers differed significantly in their judgment about child behavior and in their problem-solving abilities.38

A clinical psychological study of ten parents who battered their children severely (six of the children died) classified five as having a “high-grade mental deficiency” (mentally retarded), one as dull, and another as below average. The remaining three were classified as above average.39

A quantitative study of 113 two-parent families in the Netherlands found that parents with a high level of “reasoning complexity” (a measure of cognitive ability) responded to their children more flexibly and sensitively, while those with low levels of reasoning complexity were more authoritarian and rigid, independent of occupation and education.40

The most extensive clinical studies of neglectful mothers have been conducted by Norman Polansky, whose many years of research began with a sample drawn from rural Appalachia, subsequently replicated with an urban Philadelphia sample. He described the typical neglectful mother as follows:

She is of limited intelligence (IQ below 70), has failed to achieve more than an eighth-grade education, and has never held … employment…. She has at best a vague, or extremely limited, idea of what her children need emotionally and physically. She seldom is able to see things from the point of view of others and cannot take their needs into consideration when responding to a conflict they experience.41

The specific IQ figure Polansky mentions corresponds to the upper edge of retardation, and his description of her personality invokes further links between neglect and intelligence.

Another body of literature links neglectful and abusive parents to personality characteristics that have clear links to low cognitive ability.42 The most extensive evidence describes the impulsiveness, inconsistency, and confusion that mark the parenting style of many abusive parents.43 The abusive parents may or may not punish their children more often or severely in the ordinary course of events than other parents (studies differ on this point),44 but the abuse characteristically comes unpredictably, in episodic bursts. Abusive parents may punish a given behavior on one occasion, ignore it on another, and encourage it on a third. The inconsistency can reach mystifying proportions; one study of parent-child interactions found that children in abusing families had about the same chance of obtaining positive reinforcement for aggressive behaviors as for pro-social behaviors.45

The observed inconsistency of abusing parents was quantified in one of the early and classic studies of child abuse by Leontine Young, Wednesday’s Children. By her calculations, inconsistency was the rule in all of the “severe abuse” families in her sample, in 91 percent of the “moderate abuse” families, 97 percent of the “severe neglect” families, and 88 percent of the “moderate neglect” families.46 In one of the most extensive literature reviews of the behavioral and personality dimensions of abusive parents (as of 1985), the author concluded that the main problem was not that abusive parents were attached to punishment as such but that they were simply incompetent as parents.47

One might think that researchers seeing these malparenting patterns would naturally be inspired to look at the parents’ intelligence as a predictor. And yet in that same literature review, examining every rigorous American study on the subject, the word intelligence (or any synonym for it) does not occur until the next-to-last page of the article.48 The word finally makes its appearance as the literature review nears its end and the author turns to his recommendations for future research. He notes that in an ongoing British prospective study of parenting, “mothers in their Excellent Care group, for example, were found to be of higher intelligence … than parents in their Inadequate Care group,” and then describes several ways in which the study found that maternal intelligence seemed to compensate for other deprivations in the child’s life.49

With such obvious signals about such tragic problems as child neglect and abuse, perhaps an editorial comment is appropriate: The reluctance of scholars and policymakers alike to look at the role of low intelligence in malparenting may properly be called scandalous.


Combined with the literature, the NLSY lends further insight into good and bad parenting. We begin with information on the ways in which women of varying cognitive ability care for their children and then turn to the outcomes for the children themselves.

Prenatal Care

In most of the ways that are easily measurable, most white women in the different cognitive classes behaved similarly during pregnancy. Almost everyone got prenatal care, and similar proportions in all cognitive classes began getting it in the early months. If we take the NLSY mothers’ self-descriptions at face value, alcohol consumption during pregnancy was about the same across the cognitive classes.50 The risk of miscarriage or a stillbirth was also spread more or less equally across cognitive classes.

Smoking was the one big and medically important difference related to maternal intelligence: The smarter the women, the less they smoked while they were pregnant. Fifty-one percent of the women in the bottom two cognitive classes smoked, and 19 percent of them admitted to smoking more than a pack a day. In the top two cognitive classes, only 16 percent of the white women in the NLSY smoked at all, and only 4 percent admitted to smoking more than a pack a day. In Class I, no one smoked. Smarter pregnant women smoked less even after controlling for their socioeconomic backgrounds. Higher levels of education, independent of intelligence, also deterred pregnant women from smoking.51

Low Birth Weight

We focus here on an indicator that is known to have important implications for the subsequent health, cognitive ability, and emotional development of the child and is also affected to some degree by how well women have cared for themselves during pregnancy: low birth weight.52 Low birth weight is often caused by behaviors during pregnancy, such as smoking, drug or alcohol abuse, or living exclusively on junk food, that are seldom caused by pure ignorance these days. The pregnant woman who never registers the simple and ubiquitous lessons about taking care of herself and her baby, fails to remember them, or fails to act on them could be willfully irresponsible or in the grip of an irresistible addiction to drugs or junk food, but slow comprehension, a short time horizon, and difficulty in connecting cause and effect are at least as plausible an explanation, and all of these betoken low IQ.

A low-birth-weight baby is defined in these analyses as an infant weighing less than 5.5 pounds at birth, excluding premature babies whose weight was appropriate for their gestational age.53 The experience of the NLSY mothers is shown in the table below. There does not appear to be much of a relationship between intelligence and low birth weight; note the high rate for babies of mothers in Class I (which is discussed in the accompanying box). But the table obscures a strong overall relationship between IQ and low birth weight that emerges in the regression analysis shown in the following figure.

Low Birth Weight Among White Babies

Cognitive Class

Incidence per 1,000 Births

I Very bright


II Bright


III Normal


IV Dull


V Very dull


Population average


A white mother’s IQ has a significant role in determining whether her baby is underweight while her socioeconomic background does not


Note: For computing the plot, age and either SES (for the black curve) or IQ (for the gray curve) were set at their mean values.

A low IQ is a major risk factor, whereas the mother’s socioeconomic background is irrelevant. A mother at the 2d centile of IQ had a 7 percent chance of giving birth to a low-birth-weight baby, while a mother at the 98th percentile had less than a 2 percent chance.

Adding Poverty. Poverty is an obvious potential factor when trying to explain low birth weight. Overall, poor white mothers (poor in the year before birth) had 61 low-birth-weight babies per 1,000, while other white mothers had 36. But poverty’s independent role was small and statistically insignificant, once the other standard variables were taken into account. Meanwhile, the independent role of IQ remained as large, and that of socioeconomic background as small, even after the effects of poverty were extracted.

Can Mothers Be Too Smart for Their Own Good?

The case of low birth weight is the first example of others you will see in which the children of white women in Class I have anomalously bad scores. The obvious, but perhaps too obvious, culprit is sample size. The percentage of low-birth-weight babies for Class I mothers, calculated using sample weights, was produced by just two low-birth-weight babies out of seventy-four births.54 The sample sizes for white Class I mothers in the other analyses that produce anomalous results are also small, sometimes under fifty and always under one hundred, while the sample sizes for the middle cognitive classes number several hundred or sometimes thousands.

On the other hand, perhaps the children of mothers at the very top of the cognitive distribution do in fact have different tendencies than the rest of the range. The possibility is sufficiently intriguing that we report the anomalous data despite the small sample sizes, and hope that others will explore where we cannot. In the logistic regression analyses, where each case is treated as an individual unit (not grouped into cognitive classes), these problems of sample size do not arise.

Adding mothers age at the time of birth. It is often thought that very young mothers are vulnerable to having low-birth-weight babies, no matter how good the prenatal care may be.55 This was not true in the NLSY data for white women, however, where the mothers of low-birth weight babies and other mothers had the same mean (24-2 years).

In sum, neither the mother’s age in the NLSY cohort, nor age at birth of the child, nor poverty status, nor socioeconomic background had any appreciable relationship to her chances of giving birth to a low-birth-weight baby after her cognitive ability had been taken into account.

Adding education. Among high school graduates (no more, no less) in the NLSY, a plot of the results of the standard analysis looks visually identical to the one presented for the entire sample, but the sample of low-birth-weight babies was so small that the results do not reach statistical significance. Among the college graduates, low-birth-weight babies were so rare (only six out of 277 births to the white college sample) that a multivariate analysis produced no interpretable results. We do not know whether it is the education itself, or the self-selection that goes into having more education, that is responsible for their low incidence of underweight babies.

Infant Mortality

Though we have not been able to find any studies of cognitive ability and infant mortality, it is not hard to think of a rationale linking them. Many things can go wrong with a baby, and parents have to exercise both watchfulness and judgment. It takes more than love to childproof a house effectively; it also takes knowledge and foresight. It takes intelligence to decide that an apparently ordinary bout of diarrhea has gone on long enough to make dehydration a danger; and so on. Nor is simple knowledge enough. As pediatricians can attest, it may not be enough to tell new parents that infants often spike a high fever, that such episodes do not necessarily require a trip to the hospital, but that they require careful attention lest such a routine fever become life threatening. Good parental judgment remains vital. For that matter, the problem facing pediatricians dealing with children of less competent parents is even more basic than getting them to apply good judgment: It is to get such mothers to administer the medication that the doctor has provided.

This rationale is consistent with the link that has been found between education and infant mortality. In a study of all births registered in California in 1978, for example, infant deaths per 1,000 to white women numbered 12.2 for women with less than twelve years of education, 8.3 for those with twelve years, and 6.3 for women with thirteen or more years of education, and the role of education remained significant after controlling for birth order, age of the mother, and marital status.56

We have been unable to identify any study that uses tested IQ as an explanatory factor, and, with such a rare event as infant mortality, even the NLSY cannot answer our questions satisfactorily. The results certainly suggest that the questions are worth taking seriously. As of the 1990 survey, the NLSY recorded forty-two deaths among children born to white women with known IQ. Some of these deaths were presumably caused by severe medical problems at birth and occurred in a hospital where the mother’s behavior was irrelevant.57 For infants who died between the second and twelfth month (the closest we can come to defining “after the baby had left the hospital”), the mothers of the surviving children tested six points higher in IQ than the mothers of the deceased babies. (The difference for mothers of children who died in the first month was not quite three points and for the mothers of children who were older than 1 year old when they died, virtually zero.) The samples here are too small to analyze in conjunction with socioeconomic status and other variables.


In Chapter 5, we described how the high-visibility policy issue of children in poverty can be better understood when the mother’s IQ is brought into the picture. Here, we focus more specifically on the poverty in the early years of a child’s life, when it appears to be an especially important factor (independent of other variables) in affecting the child’s development.58 The variable is much more stringent than simply experiencing poverty at some point in childhood. Rather, we ask about the mothers of children who lived under the poverty line throughout their first three years of life, comparing them with mothers who were not in poverty at any time during the child’s first three years. The standard analysis is shown in the figure below. There are few other analyses in Part II that show such a steep effect for both intelligence and SES. If the mother has even an average intelligence and average socioeconomic background, the odds of a white child’s living in poverty for his or her first three years were under 5 percent. If either of those conditions fell below average, the odds increased steeply.

A white mother’s IQ and socioeconomic background each has a large independent effect on her child’s chances of spending the first three years of life in poverty


Note: For computing the plot, age and either SES (for the black curve) or IQ (for the gray curve) were set at their mean values.

The Role of Preexisting Poverty

When we ask whether the mother was in poverty in the year prior to birth, it turns out that a substantial amount of the effect we attribute to socioeconomic background in the figure really reflects whether the mother was already in poverty when the child was born. If you want to know whether a child will spend his first three years in poverty, the single most useful piece of information is whether the mother was already living under the poverty line when he was born. Nevertheless, adding poverty to the equation does not diminish a large independent role for cognitive ability. A child born to a white mother who was living under the poverty line but was of average intelligence had almost a 49 percent chance of living his first three years in poverty. This is an extraordinarily high chance of living in poverty for American whites as a whole. But if the same woman were at the 2d centile of intelligence, the odds rose to 89 percent; if she were at the 98th centile, they dropped to 10 percent.59 The changes in the odds were proportionately large for women who were not living in poverty when the child was born.

The Role of Education

For children of women with a high school diploma (no more, no less), the relationships of IQ and socioeconomic background to the odds that a child would live in poverty are the same as shown in the figure above—almost equally important, with socioeconomic background fractionally more so—except that the odds are a little lower than for the whole sample (the highest percentages, for mothers two standard deviations below the mean, are in the high 20s, instead of the mid-30s). As this implies, the highest incidence of childhood poverty occurs among women who dropped out of school Among the white college sample (a bachelor’s degree, no more and no less), there was nothing to analyze; only one child of such mothers had lived his first three years in poverty.


In 1986, 1988, and 1990, the NLSY conducted special supplementary surveys of the children and mothers in the sample. The children were given tests of mental, emotional, and physical development, to which we shall turn presently. The mothers were questioned about their children’s development and their rearing practices. The home situation was directly observed. The survey instruments were based on the so-called HOME (Home Observation for Measurement of the Environment) index.60

Dozens of questions and observations go into creating the summary measures, many of them interesting in themselves. Children of the brightest mothers who also tend to be the best educated and the most affluent) have a big advantage in many ways, especially on such behaviors as reading to the child. On other indicators that are less critical in themselves, but indirectly suggest how the child is being raised, children with smarter mothers also do better. For example, mothers in the top cognitive classes use physical punishment less often (though they agree in principle that physical punishment can be an appropriate response), and the television set is off more of the time in the homes of the top cognitive classes.

Treating the HOME index as a continuous scale running from “very bad” to “very good” home environments, the advantages of white children with smarter mothers were clean The average child of a Class V woman lived in a home at the 32d percentile of home environment, while the home of the average child of a Class I woman was at the 76th percentile. The gradations for the three intervening classes were regular as well.61 Overall, the correlation of the HOME index with IQ for white mothers was +.24, statistically significant but hardly overpowering.

In trying to identify children at risk, this way of looking at the relationship is not necessarily the most revealing. We are willing to assume that a child growing up in a home at the 90th centile on the HOME index has a “better” environment than one growing up at the 50th. Perhaps the difference between a terrific home environment and a merely average one helps produce children who are at the high end on various personality and achievement measures. But it does not necessarily follow that the child in the home at the 50th centile is that much more at risk for the worst outcomes of malparenting than the child at the 90th centile. Both common sense and much of the scholarly work on child development suggest that children are resilient in the face of moderate disadvantages and obstacles and, on the other hand, that parents are frustratingly unable to fine-tune good results for their children.

But resilience has its limits. Children coming from the least nurturing, most punishing environments are indeed at risk. We will therefore focus throughout this section on children who are in the bottom 10 percent on various measures of their homes.62

Which White Children Grow Up in the Worst Homes?

Cognitive Class of the Mother

Percentage of Children Growing Up in Homes in the Bottom Decile of the HOME Index

I Very bright


II Bright


III Normal


IV Dull


V Very dull


All whites


In the case of the HOME index, the percentages of white children of mothers in the different cognitive classes who are growing up in homes that scored at the bottom are displayed in the table above. It was extremely rare for children of women in the top cognitive classes to grow up in these “worst homes” and quite uncommon for children of women throughout the top three-fourths of the IQ distribution. Only in the bottom cognitive classes did the proportion of such children grow, and then the proportions rose rapidly. Nearly one out of four of the children of the dullest mothers was growing up in a home that also ranked in the bottom decile on the HOME index.63

The Role of Socioeconomic Background

The usual assumption about maternal behavior is that a woman’s socioeconomic status is crucial—that she passes on to her children the benefits or disadvantages of her own family background. The figure below summarizes the standard analysis comparing SES and IQ.

A white mother’s IQ is more important than her socioeconomic background in predicting the worst home environments


Note: For computing the plot, age and either SES (for the black curve) or IQ (for the gray curve) were set at their mean values. Additional independent variables were used to control for the test year and the age of the children.

Both factors play a significant role, but once again it is worse (at least for the white NLSY population) to have a mother with a low IQ than one from a low socioeconomic background. Given just an average IQ for the mother, even a mother at the 2d centile on socioeconomic background had less than a 10 percent chance of providing one of the “worst homes” for her children. But even with average socioeconomic background, a mother at the 2d centile of intelligence had almost a 17 percent chance of providing one of these “worst homes.”

The Role of Poverty and Welfare

Many of the problems experienced by poor children are usually attributed in both public dialogue and academic writings to poverty itself.64 The reasons for this widely assumed link between poverty and developmental problems are harder to spell out than you might think. To repeat a point that must always be kept in mind when thinking about poverty: Most of the world’s children throughout history have grown up poor, with “poverty” meaning material deprivation far more severe than the meaning of “below the poverty line” in today’s America. Many of the disadvantages today’s children experience are not the poverty itself but the contemporary correlates of poverty: being without a father, for example, or living in high-crime neighborhoods. Today, high proportions of poor children experience these correlates; fifty years ago, comparatively few poor children did.

But there are reasons to think that the HOME index might be influenced by poverty. Reading to children is a good thing to do, for example, and raises the HOME score, but children’s books are expensive. It is easier to have books in the house if you can afford to buy them than if you have to trek to the library—perhaps quite far from home—to get them. Similar comments apply to many of the indicators on the HOME index that do not require wealth but could be affected by very low income. We therefore explored how the HOME index was related to the mother’s poverty or welfare recipiency in the calendar year before the HOME score was obtained.65

Poverty proved to be important, with “being in a state of poverty” raising the odds of being in the worst decile of the HOME index from 4 percent to 11 percent, given a mother of average IQ and socioeconomic status.66 But adding poverty to the equation did not diminish the independent role of cognitive ability. For example, if the mother had very low IQ (the 2d centile) and was in poverty, the odds of being in the worst decile on the HOME index jumped from 11 percent to 26 percent. Generally, adding poverty to the analysis replaced the impact of the mother’s socioeconomic background, not of her intelligence.

Then we turn to welfare. The hypothesis is that going on welfare signifies personality characteristics other than IQ that are likely to make the home environment deficient—irresponsibility, immaturity, or lack of initiative, for example. Therefore, the worst homes on the HOME index will also tend to be welfare homes. This hypothesis too is borne out by the data: Welfare recipiency was a slightly more powerful predictor of being in a “worse home” than poverty—but it had as little effect on the independent role of IQ.

In trying to decide among competing explanations, the simplest thing to do is to enter both poverty and welfare in the analysis and see which wins out. We summarize the outcome by first considering a child whose mother is of average intelligence and socioeconomic background. If his mother is either poor or on welfare (but not both), the odds of having a terrible home environment (bottom decile on the HOME index) are 8 or 9 percent. If the mother has an IQ of 70, the odds shoot up to 18 to 21 percent. If the mother has very low intelligence, is poor, and is also on welfare, the odds rise further, to 34 percent. A table with some of the basic permutations is given in the note.67

Still, many of the causal issues remain unresolved. The task for scholars is to specify what it is about poverty that leads to the outcomes associated with it. With the data at hand, we cannot go much further in distinguishing between the effects of lack of money and the effects of other things that “being in poverty” signifies. In particular, the way that poverty and welfare interact in producing a poor home environment provides many hints that need to be followed up.

What can be said unequivocally is that low income as such does not prevent children from being raised in a stimulating, nurturing environment. Such is the story of the regression coefficients, and a conclusion that accords with child rearing throughout history. By the same token, it does not take a genius to provide a child with a stimulating, nurturing environment. The average differences in environment across the cognitive classes are large and in many ways troubling, but, in percentage terms, they explain little of the variance. Abundant examples of excellent parents may be found through all but the very lowest range of cognitive ability.

The Role of Education

We conclude, as usual, by considering the role of education through the high school graduate and college graduate subsamples. Holding maternal age and the mother’s socioeconomic background constant at their means, college graduates tend to do well, no matter what their cognitive ability (within their restricted range), even though cognitive ability retains a statistically significant relationship. Within the high school sample, the effects of cognitive ability are plain; the odds of being in the bottom decile on the HOME index for the child of a mother of average socioeconomic background drop from 15 percent for a high school graduate at the 2d IQ centile to 5 percent for a comparable person at the 98th IQ centile. As in the earlier analyses, the most important impact of cognitive ability within the high school graduates seems to be at the low end. Socioeconomic background also continues to play an important independent role, but less than IQ.

Some More Complications

The HOME inventory has two components—a Cognitive Stimulation score and an Emotional Support score—both adapted to three separate age groups (under 3, 3 to 5, and over 5 years of age). We conducted a variety of analyses to explore the subtests’ roles for different age groups. Briefly, the mother’s IQ had the dominant role in determining the Emotional Support score for children through the age of 5, whereas its role in determining Cognitive Stimulation was roughly coequal with education and socioeconomic background—the opposite of what one might predict. Maternal IQ was especially important for Emotional Support to the 3- to 5-year-old group. It would be worthwhile for investigators to explore with other data the NLSY’s indications that parental IQ is especially important for the home environment from ages 3 to 5, and the peculiar finding that parental IQ is more important for Emotional Support than for Cognitive Stimulation.


The NLSY also administered batteries of tests regarding the developmental outcomes for the children of NLSY mothers. We review several indicators briefly, then present a summary index showing the interrelationships the mother’s cognitive ability, socioeconomic background, poverty, and welfare.

Temperament in Very Young Children

The first of the measures applies to very young children (12 to 23 months), and consists of indexes of “difficulty” and “friendliness.” Once again we focus on children who exhibit the most conspicuous signs of having problems—those in the bottom decile—as shown in the following table.68 Generally, babies were more “difficult”—more irritable, more fearful, and less sociable—for mothers with lower cognitive ability, and they were also less friendly, as measured by this index.

Which White Toddlers Have the Worst Temperaments?

Percentage of Children in the Most Difficult Decile on the Difficulty Index

Cognitive Class of the Mother

Percentage of Children in the Least Friendly Decile on the Friendliness Index

I Very bright


II Bright



III Normal



IV Dull


V Very Dull



All Whites


Motor and Social Development in Infants and Toddlers

Motor and social development is, in effect, a set of measures designed to capture whether the child is progressing in the ways described as normal in the baby manuals by Spock, Brazelton, et al The table below shows the results for children through the age of 3. The results look like a U-shaped curve, with a big jump in Class V Since sample sizes in both Class I and Class V are under 100 (75 and 81, respectively), this information falls in the category of interesting but uncertain.

Behavioral Problems in Older Children

For older children, the NLSY employed an instrument that measured behavioral problems, with subscales on antisocial behavior, depression, headstrongness, hyperactivity, immature dependency, and peer conflict/social withdrawal. The table below shows the results for those who had the most severe problems—those in the worst 10 percent on these measures.

Which White Children Are Behind in Motor and Social Development?

Cognitive Class of the Mother

Percentage of Children in the Bottom Decile of the Motor & Social Development Index

I Very bright


II Bright


III Normal


IV Dull


V Very dull


All whites


Which White Children Have the Worst Behavioral Problems?

Cognitive Class of the Mother

Percentage of Children in the Worst Decile of the Behavioral Problems Index

I Very bright


II Bright


III Normal


IV Dull


V Very dull


All whites


Once again, there is the curious case of the elevated percentage for children of mothers in Class I. The most prudent assumption is that it is an artifact of small sample sizes, but the possibility remains that something else is going on worth investigating in greater detail, with larger samples.

An Index of Developmental Problems

Each of the developmental indexes we have reviewed is based on a number of individual items, which in turn lend themselves to a wide variety of analyses that would take us far beyond the scope of this discussion. We conducted many analyses for the separate indexes, but the overall patterns were similar. For our purposes in conveying to you the general pattern of results, it is sufficient to summarize the results for a broad question: What independent role, if any, does the mother’s IQ have on the probability that her child experiences a substantial developmental problem? We created a simple “developmental problem index,” in which the child scores “Yes” if he or she were in the bottom decile of any of the four indicators in a given test year, and “No” if not. The results are shown in the next figure.

Both a white mother’s IQ and socioeconomic background have moderate relationships with developmental problems in the child


The pattern shown in the figure generally applies to the four development indicators separately: IQ has a somewhat larger independent effect than socioeconomic background, but of modest size and marginal statistical significance.

The Role of Poverty, Welfare, and Illegitimacy

We repeated the analyses adding a poverty variable (Was the mother living in poverty in the year the developmental measures were taken?), a welfare variable (Was the mother on AFDC in the year the developmental measures were taken?), and legitimacy variable (Was the child born outside marriage?) When entered separately or in combination, each had a statistically significant independent role.69 Consider the stark contrast between a child born to an unmarried mother, on welfare and in poverty, and a child born to a married mother, not on welfare and above the poverty line. Given a mother with average IQ and socioeconomic background, the chances that the first child had a substantial developmental problem were almost twice as high as those facing the second child—15 percent compared to 8 percent. But taking these factors into account did not wipe out the independent role of either IQ or the mother’s socioeconomic background; in fact, the independent effects of IQ and socioeconomic background after extracting the independent role of poverty, illegitimacy, and welfare, are visually almost indistinguishable from the one shown above.

The Role of Education

Analyses of the college graduate sample were provocative but no more than that, because only 29 out of 470 children of white college graduates who were tested (6 percent) showed up with a substantial developmental problem. The provocative finding was that among those 29, 5 were children of women in Class 1(10 percent of the 50 such children tested). Thus in the college sample, the statistical result of holding socioeconomic background constant was that higher IQ was associated with a substantially higher probability of having developmental problems. Five out of 50 is of course not enough to make much of these numbers, but we commend the finding to our colleagues who specialize in child development.

Within the high school sample, the independent roles of IQ and socioeconomic background were almost identical, and of the same order of magnitude indicated in the figure for the entire white sample.


We finally come to the intelligence of the children of white NLSY women. The measure of intelligence we shall be using is the Peabody Picture Vocabulary Test (PPVT), a widely used measure of cognitive ability in children that has the advantage of not requiring that the child be able to read. The scores for the NLSY children are expressed in terms of the national norms for the PPVT, which use a mean of 100 and a standard deviation of 15. Because IQ scores tend to be volatile for children under the age of 6, we limit the sample to children who were at least 6 when they took the test.

The unsurprising news in the next table is that the children tend to resemble their mothers in IQ.70 But by continuing to use the “worst decile” as a way of zeroing in on the children most at risk, the table makes another point: White parents throughout the top three-quarters of the IQ distribution have few children who fall into the bottom decile of IQ.71 For mothers in the bottom quarter of the distribution, however, the proportion of low IQ children rises precipitously. We return to this issue in Chapter 15.

IQ in the Mother and the Child for Whites in the NLSY

Cognitive Class of the Mothers

Mean IQ of Their Children

Percentage of Their Children in the Bottom Decile of IQ

I Very bright

II Bright



III Normal



IV Dull



V Very dull



All whites



The Role of Socioeconomic Background

Consistent with the conclusions drawn in a large technical literature, the IQ of the NLSY mothers was much more important than their socioeconomic background in determining their children’s IQ.72 A white child’s IQ in the NLSY sample went up by 6.3 IQ points for each increase of one standard deviation in the mother’s IQ, compared to L 7 points for each increase of one standard deviation in the mother’s socioeconomic background (in an analysis that also extracted the effects of the mother’s age, the test year, and the age of the child when tested). When we examine the probability that the child will fall in the bottom decile of IQ, we arrived at the results shown in the next figure.

A white mother’s IQ dominates the importance of socioeconomic background in determining the child’s IQ


Note: For computing the plot, age and either SES (for the black curve) or IQ (for the gray curve) were set at their mean values. Additional independent variables were used to control for the test year and the age of the children when they took the test.

A mother at the 2d IQ centile but of average socioeconomic background had a 30 percent chance that her child would be in the bottom decile of IQ, compared to only a 10 percent chance facing the woman from an equivalently terrible socioeconomic background (2d centile on the SES index) but with an average IQ.

The Role of Poverty and the Home Environment

In discussions of IQ among disadvantaged groups, it seems plausible that factors such as poverty and the aspects of the home environment would have an effect on the child’s IQ. Suppose, for example, we were to ignore the mother’s IQ, and look only at her socioeconomic background, her poverty status in the year before her child was tested, and her HOME index score. In that case, we could document the conventional wisdom: both socioeconomic background and the home environment have large effects on whether a child scores in the bottom IQ decile. Poverty has a smaller and statistically marginal effect. But when we add the mother’s IQ, all of those other effects become both small in magnitude and statistically insignificant. After taking socioeconomic background, the HOME index, and pretest poverty into account, the independent effect of IQ remains virtually identical to the one shown on the preceding figure.

The Role of Education

None of the children in the bottom decile of IQ had a mother with a bachelor’s degree. In the high school graduate sample, the independent role of the mother’s IQ remains large and the independent role of socioeconomic background remains small. But in the process of exploring this issue, we came upon an effect of education that is worth exploring: Women who did not complete high school were at much higher risk of producing children in the bottom decile of IQ than women in the high school sample (meaning a high school diploma and exactly 12 years of education), even after controlling for mother’s IQ and socioeconomic background. Additional analyses did not clarify what this finding might mean; we commend it to our colleagues for a full-scale analysis.


Granting the many exceptions at the individual level, the relationship of cognitive ability to parenting is unmistakable. Some of these analyses have involved measures that are arguable. Can we really be sure that the indicators of what constitutes a stimulating and nurturing environment are not just reflections of the preferences of the upper middle class? We hope our readers do not take this easy way out. If the indicators that were used in the studies we have reported are indeed ones that you find valid in your own beliefs about what children need, then the conclusion follows: Over the long run and in the broad perspective, based on your best understanding of the realities of child rearing, smart parents tend to be better parents. People with low cognitive ability tend to be worse parents. This conclusion holds for a wide range of parenting behaviors, from prenatal negligence that leads to low birth weight, to postnatal treatment of the child associated with neglect and abuse, to developmental outcomes, to cognitive outcomes.

On the other hand, these data provide little or no evidence that the smartest women make the best mothers. Children can flourish in a wide variety of environments that are merely okay. But some environments are so bad that no one can seriously dispute that they are bad, and even the most resilient children have difficulty overcoming them. These truly disadvantaged homes are disproportionately associated with women at the low end of the intelligence distribution, even after other contributing factors such as poverty and socioeconomic status are taken into account.