Journals > Journal: School Readiness: Closing Racial and Ethnic Gaps > Article: Health Disparities and Gaps in School Readiness
Journal Issue: School Readiness: Closing Racial and Ethnic Gaps Volume 15 Number 1 Spring 2005
Health Conditions and School Readiness
This section considers several specific types of health problems including child mental health problems, chronic physical conditions, environmental hazards, and poor nutrition. The impact of maternal health conditions and behaviors is considered in the next section.
Child Mental Health Problems
According to the 1999 U.S. surgeon general's report, approximately one in five children and adolescents in the United States has symptoms of mental or behavioral disorders. Attention deficit hyperactivity disorder, the most commonly diagnosed chronic mental health problem among young children, is the focus of this section. The disorder is characterized by an inability to pay attention (inattention) or by hyperactivity, or both.2
Children with ADHD are not school ready, almost by definition. They have great difficulty with basic tasks such as sitting still and listening to instructions. They are likely to be disruptive and to have trouble getting along with other children because, for example, they constantly interrupt and have trouble taking turns. The disorder is also often linked with cognitive impairments.
A diagnosis of ADHD has three main criteria. Six or more symptoms of inattention or of hyperactivity must persist for at least six months to a degree that is maladaptive and inconsistent with the child's developmental level. Some of the symptoms must be present before the child reaches the age of seven. And impairment from the symptom must be evident in two or more settings, such as home and school. This last criterion means that teachers are often important for the diagnosis of ADHD.3
Assessing the prevalence of ADHD is complicated. Most studies of its prevalence are based on diagnosed cases, but considerable controversy exists over whether the disorder is over- (or under-) diagnosed. Data from the National Institute of Mental Health's Epidemiology of Child and Adolescent Mental Health Disorders (MECA) study of 1,285 youths aged nine through seventeen indicate that 5.1 percent of the children had ADHD. A study of 21,065 children aged four to fifteen recruited from 401 family medical practices found that 9.2 percent had “attention deficit-hyperactivity problems” according to their clinician, but that the clinicians did not generally use standard diagnostic criteria.4
According to the hyperactivity subscale of the Strengths and Difficulties Questionnaire of the National Health Interview Survey, 4.19 percent of boys and 1.77 percent of girls have “clinically significant” ADHD symptoms. Among boys, the prevalence is highest among blacks, at 5.65 percent, as against 4.33 percent for whites and 3.06 percent for Hispanics. Prevalence is also higher (6.52 percent) in families with incomes less than $20,000 than in families with higher incomes (3.85 percent). When gender, race, age, income, and parental education are taken into account, the effect of income remains statistically significant, but there is no difference in prevalence between blacks and whites.5
Although drug therapy improves behavior for approximately 70 to 80 percent of ADHD children, the evidence that treatment affects academic performance is much less conclusive.6 Treatment differs widely by race and income. Data from the National Health Interview Survey indicate that the share of parents who had ever been told that their child had ADHD was 7.5 percent for whites, 5.7 percent for blacks, and 3.5 percent for Hispanics. For poor children the rates were 7.1 percent as against 6.6 percent for nonpoor children. According to the 1997 Medical Expenditure Panel, 4.4 percent of whites but only 1.7 percent of blacks were treated for ADHD, though the probability of receiving treatment varied little by income. In a Maryland study of Medicaid patients, blacks were less than half as likely to have been prescribed psychotropic drugs as whites were, indicating that even among children with similar insurance coverage, treatment patterns differ by race.7
In one study, teachers were given profiles of students and asked whether they had ADHD. The race and gender assigned to the profiles were randomly varied. Teachers were most likely to believe that white males had ADHD and least likely to think that white females had the disorder, with black students falling in between. A study based on random telephone interviews found that in a sample of 381 high-risk children, 91 percent of the white parents and 85 percent of the black parents believed that their child had a problem. Fifty-one percent of the white children had been evaluated for ADHD as against only 28 percent of the black children. Rates of treatment were 31 percent for whites and 15 percent for blacks. Following up on children who were diagnosed but not treated, the researchers found that blacks were more likely than whites to cite negative expectations about the treatment (58 percent versus 34 percent), stigma (47 percent versus 32 percent), and financial constraints (32 percent versus 15 percent).8
Using survey data that followed a group of children from the United States and Canada, Mark Stabile and I show that children with ADHD not only perform more poorly than children without the disorder on cognitive tests, but also are at greater risk of having to repeat a grade and to enroll in special education, even after controlling for a wide range of potential confounders. ADHD affects cognition and behavior more than other chronic health conditions, such as asthma, or poor health generally. Our estimates imply that children with ADHD score at least a quarter of a standard deviation lower on standardized tests of mathematics and reading than other children. Surprisingly, the effect of ADHD on cognitive and scholastic outcomes is not strongly related to income in either country.9
How much of the racial gap in school readiness might be accounted for by ADHD? Suppose that a generic test has a mean of 50 and a standard deviation of 15 and that black children tend to score at least a half a standard deviation (8 points) lower than white children on this test. The studies discussed above suggest that ADHD lowers test scores by about a third of a standard deviation (5 points) and that about 4 percent of whites have the disorder, compared with 6 percent of blacks. Hence, if the difference in the prevalence of ADHD were the only difference between the black and white children, one would expect the average test score of a sample of white children to be 49.8, while the average test score of a sample of black children would be 49.10
This estimate, though crude, makes clear that the mean test scores of blacks and whites are driven by children who do not have any health conditions. That being so, any given health condition would have to have quite a large effect (or a very different prevalence for whites and blacks) before it could have much effect on mean differences in test scores.
Chronic Physical Health Conditions
Poor children are more likely than better-off children to suffer from a wide array of chronic health problems, particularly severe conditions such as mental retardation, heart problems, poor hearing, and digestive disorders. Chronic conditions affect school readiness in various ways. First, illness may simply crowd out other activities with doctor visits and treatment. Second, children with chronic conditions may experience more stress, fatigue, or pain that can interfere with cognitive development. Third, drugs used to treat some illnesses may have unanticipated effects. Fourth, illness may alter relations between children, parents, and others in a way harmful to the child's development. Fifth, illnesses directly affect the ability to learn, by altering body chemistry.11
This section focuses on asthma. Not only is asthma one of the most common chronic conditions among children, but it is also the subject of much research focused both on black-white gaps in prevalence and on the relationship between asthma and measures of cognitive achievement and behavior.
Asthma is the leading cause of children's trips to the emergency room, of their being hospitalized, and of their being absent from school. An “asthmatic” child is one who has had an episode of blocked airways or who has a tendency toward such episodes. Doctors use different methods to diagnose asthma, and diagnosis depends on the child's either having an episode or being treated for breathing or wheezing problems. Children whose asthma is adequately managed should not have acute attacks. Prevalence surveys that focus on doctor diagnoses and those that focus on asthma attacks, therefore, lead to very different estimates.
According to the 2001 National Health Interview Survey (NHIS), 13 percent of children under age eighteen have been diagnosed with asthma, and 6 percent have had an asthma attack in the past twelve months. Prevalence rates in diagnosed asthma are higher for blacks (15.7 percent) than for whites (12.2 percent) but lowest for Hispanics (11.2 percent). Rates are also higher for poor children (15.8 percent) than nonpoor children (12 percent). Among black children, 7.7 percent had an attack in the past twelve months, as against 5.7 percent of whites and only 4 percent of Hispanics.12
The NHIS further shows that 1.6 percent of white children under age eighteen, and 5.7 percent of black children, had been hospitalized for asthma between 1998 and 1999. The disparity in hospitalizations is much greater than that in the number of attacks, suggesting that black children's asthma is either much more serious or much less likely to be controlled. This conclusion is supported by the finding that blacks were more likely than whites to have their activity limited because of asthma (32.7 percent compared with 21.4 percent). Similar disparities in morbidity were noted between poor and nonpoor children (33.2 percent vs. 20.8 percent), but poor black children were most likely to have activity limited because of asthma (49 percent as against about 20 percent for nonpoor black or white children or for poor white children).13
Consistent with these observations, several smaller-scale studies have noted that doctors are less likely to prescribe inhaled antiinflammatory drugs for minorities than for whites. One study using nationally representative data from the National Health and Nutrition Examination Survey (NHANES) III focuses on children with moderate to severe asthma (defined as having been hospitalized or having two or more acute attacks or three or more episodes of wheezing over the past year) and finds that only 26 percent of these children were taking maintenance medication. In this group, children who have Medicaid insurance and who speak Spanish are more likely to be inadequately medicated for asthma. Race is not an independent factor.14
Many research papers suggest, perhaps surprisingly, that asthma has little effect on cognitive outcomes or schooling attainment. Most such studies, however, examine children whose asthma is well controlled. Indeed, the purpose of such studies is to see whether the medication children take to control their asthma affects their cognitive functioning. But several studies indicate that children with asthma are more likely than other children to have behavior problems, even when the asthma is controlled. For example, one study found that asthmatic children scored between two-thirds to one standard deviation below the normative value on a test of impulse control, while another found that asthma doubled the risk of behavioral problems. These changes in behavior may reflect relatively subtle effects of childhood illness on parenting and family functioning.15
One large population-based study using NHIS data found that asthma affected school absences, the probability of having learning disabilities, and grade repetition. Asthmatic children in grades one to twelve were absent from school an average of 7.6 days a year as against 2.5 days for well children. Nine percent of the asthmatic children (5 percent of the well children) had learning disabilities; 18 percent (15 percent of the well children) repeated a grade.16
In the only study to examine school readiness explicitly, Jennifer Halterman and her collaborators examine 1,058 children entering kindergarten in urban Rochester and find that asthmatic children had lower scores on a test of school readiness skills and that their parents were three times more likely to report that they needed extra help with learning. Tests of language, motor, and socio-emotional skills showed no differences. The negative effects were concentrated among a group of children whose asthma was severe enough to limit their activity (suggesting that it was not adequately controlled), a group more likely to include boys than girls.17
One difficulty in interpreting all these studies is that because asthma is most prevalent among poor and minority children, the apparent effect of asthma on academic performance and behavior could reflect omitted third factors. But several studies of homogeneous groups of children also find differences in behavior, suggesting that asthma probably does have a causal effect at least on behavior problems and hence on school readiness.
A back-of-the-envelope calculation similar to that for ADHD can help determine whether these differences are large enough to affect the mean test score gap. The studies discussed above suggest that some 5 percent of black children, but only 3 percent of white children, have asthma severe enough to limit their activity. The major effect of asthma is on behavior, so I will assume that asthmatic children score a standard deviation higher on a behavior-problem index than do non-asthmatic children and that the index has the same characteristics as the generic test score assumed above (that is, mean of 50, standard deviation of 15, average black-white difference of 8). Under these assumptions, the average behavior-problem score among blacks would be 50.4; that among whites, 50.2. Again, although asthma has important effects on individual children, it cannot account for much of the racial gap in measures of school readiness.18
Environmental Exposures to Hazardous Substances
The literature on asthma strongly suggests that its greater prevalence among impoverished children could be due in part to characteristics of their housing. The degree of segregation by race, ethnicity, and income in American cities suggests that some groups are more likely than others to be exposed to environmental hazards. Moreover, to the extent that known environmental hazards are capitalized into housing prices, pollution will lower rents, making hazardous areas more attractive to poor people than to rich ones. Conversely, low land prices in poor neighborhoods may draw in new hazards. One environmental hazard whose effect on children's health has been studied extensively is lead.
Lead has long been known to be toxic. Blood lead levels above 45 micrograms per deciliter (microg/dl) can cause damage to the central nervous system and even death. For many years, the Centers for Disease Control set 30 microg/dl as the threshold “level of concern” for lead poisoning. But in response to evidence that levels as low as 10 microg/dl could affect children's cognitive functioning and behavior, the CDC lowered the threshold to 25 microg/dl in 1985 and to 10 microg/dl in 1991. Controversy now centers on whether even lower levels of lead endanger children, who are generally at higher risk from lead than adults. In adults only organic lead compounds can breach the blood-brain barrier; in children, both organic and inorganic lead can penetrate that barrier. And children who have diets deficient in calcium, iron, and zinc tend to absorb more lead.19
Before the federal government began to regulate lead, children were exposed to it in paints, in drinking water (from lead solder in pipes), in gasoline, and in canned food. According to the NHANES surveys, 88.2 percent of children aged one to five had lead levels above 10 microg/dl during 1976–80. That share plummeted to 8.6 percent during 1988–91 and fell further to 2.2 percent during 1999–2000—figures that imply that the number of children with unsafe lead levels fell from 13.5 million to less than half a million over this period.20
Still, lead remains in the soil, in paint in older homes, and in pipes. Some states still have lead “hot spots.” One study reported that 68 percent of children attending a pediatric clinic in inner-city Philadelphia had unsafe levels of lead in their blood. Poor and black children are more likely than others to have unsafe levels.21
The NHANES data from 1999–2000 and data from state surveillance systems indicate that 60 percent of one- to five-year-old children with confirmed elevated blood lead levels between 1997 and 2001 were black, indicating a much higher prevalence among blacks than among whites. In 2001, 2 percent of white children and 8.7 percent of black children had confirmed high blood lead levels. The condition affects more boys than girls. In 2001, for example, 40,000 boys and 33,000 girls were confirmed to have high levels.22
Although some studies have found that increasing blood lead levels from 10 to 20 microg/ dl reduces IQ scores by as much as 7 points (where one standard deviation is about 15 points), two reviews of many studies of blood lead levels conclude that such an increase would reduce IQ by about 2 points. Elevated lead levels have also been linked to hyperactivity and behavior problems, most famously by Herbert Needleman, who argues that lead exposure causes criminal behavior. In his study, a sample of delinquents was four times more likely to have high bone lead levels than a group of matched controls. But because lead exposure is increasingly strongly correlated with minority status, poverty, and residence in decaying older neighborhoods, it is possible that at least some of the observed correlations between lead levels and negative outcomes reflect omitted third factors. These estimates of the effects of low-level lead exposure should thus be regarded as upper bounds.23
A calculation similar to those made for ADHD and asthma suggests that differing exposure to lead might be responsible for 0.2 point of the average eight-point racial gap in scores assumed above. If racial disparities in exposure to other environmental hazards have also grown, exposure to such hazards could be an increasingly important cause of disparities in school readiness.24
Nutrition
U.S. food and nutrition programs were created to ensure that children and other vulnerable people would get enough to eat. Only recently have researchers and policymakers begun to recognize that many if not most children eat too much of the wrong things and that obesity is a greater threat to child health than insufficient calories. In fact, children at risk of missing meals (those who are “food insecure”) are more likely to be obese than other children, although they are also more likely to be lacking specific micronutrients. Similarly, poor children from birth to age five are twice as likely as betteroff children to be obese, about a third more likely to be anemic, and about 20 percent more likely to be deficient in vitamin A. It is possible that many micronutrients will be found to affect cognitive development among young children. But because most research to date on the effects of nutrition on cognition has focused on iron-deficiency anemia, that will be the focus of this section.25
Among its many negative effects on health, iron deficiency impairs immune function, cognitive functioning, and energy metabolism. Clinically, iron deficiency is defined as having an abnormal value on at least two out of three laboratory tests of iron status. Anemia, a more severe condition, is defined as iron deficiency plus low hemoglobin.
When infants are about four months old, they begin to deplete the stores of iron with which they are born. The widespread use of iron-fortified infant formula and cereals has made anemia much less of a problem in infants under one year. But toddlers may stop eating these iron-fortified infant foods before they begin to gain adequate iron from their diet.
According to the NHANES III, 9 percent of toddlers are iron deficient, as against 3 percent of three- to five-year-olds and 2 percent of six- to eleven-year-olds. Only 3 percent of toddlers are anemic, and less than 1 percent of children aged three to eleven are anemic. The NHANES 1999–2000 yields similar estimates. These anemia rates are down considerably from 15–30 percent in the late 1970s and early 1980s, a decline variously attributed to iron-fortified foods and the growth of the Special Supplemental Nutrition Program for Woman, Infants, and Children (WIC), a federal program that offers food supplements to pregnant, lactating, and postpartum mothers, infants, and children younger than five.26
Iron deficiency is much more common among poor and black children than among other children. Twice as many black children as white children are iron deficient (16 percent versus 8 percent for toddlers), while poor children are more than 50 percent more likely to be deficient than nonpoor children. If iron deficiency impairs cognitive functioning, it could well be responsible for part of the test score disparities between blacks and whites and between poor and nonpoor children.
Sally Grantham-McGregor and Cornelius Ani reviewed observational studies that followed a group of children over time and found that conditional on measures of social background, gender, and birth weight, low hemoglobin levels in children aged two or younger are strongly linked to poor schooling achievement, cognitive development, and motor development in middle childhood. These studies, however, do not establish a causal relationship, given the strong association between iron deficiency and other factors that could affect development, such as poverty.27
Grantham-McGregor and Ani also survey studies of trials in which anemic or iron-deficient children were given iron supplements. They find that giving anemic children iron supplements for two to six months improves cognitive functioning, although not enough to allow school-age children to up to their non-anemic peers. Five small-catch-scale studies (four in developing countries) that investigated the effect of iron supplementation on iron-deficient non-anemic children found little evidence of an effect on cognition, but it is possible that subtle effects of improving iron status in these samples of children without anemia might be detectable in larger samples.
In short, although the higher rates of iron deficiency among poor and minority children are a cause for concern, little concrete evidence links these disparities to gaps in cognitive outcomes or schooling attainment. Anemia itself, which has been more definitively linked to cognitive deficits and poorer schooling attainment, has become relatively rare, even among disadvantaged children. Although anemia may have contributed to the readiness gap in the past, it is unlikely to be a major contributor today.
