Study attempts to separate health from social influences on brain development

To find a group of healthy children, the NIH researchers screened more than 35,000 youngsters for medical, neurologic and psychiatric disorders, as well as for family histories that point to potential problems or prenatal exposure to toxins. Only 450 of the children met the strict criteria.

Income predicted IQ and academic achievement. Lower income was associated with lower IQ scores (mean IQs were 105, 110, and 115 for low-, middle- and high-income children respectively). Lower-income children were more likely to be excluded from the study because of medical or developmental conditions; the healthy low-income children who qualified performed, on average, better than previously reported population averages. "We were pleasantly surprised by how well the lower-income children did when we focused on those who were healthy," says Waber. Although income did not predict performance on basic cognitive tasks, such as memory or reading individual words, lower-income children did score lower on tests like reading comprehension and calculation. The authors suggest that such tasks, which require more reasoning and integration of cognitive abilities, are more vulnerable to the effects of poverty-related factors than are more basic skills.