no documented biomedical cause has been observed at elevated levels among very poor families (Garber, 1988).

For any individual child, genetic and experiential information come together in a process that organizes the brain to function. An NRC report on the science of early childhood development lists environmental factors that play a significant role in modulating prenatal and early postnatal brain development (see NRC, 2000a:199). The list, although not exhaustive, includes factors selected on the basis of clinical importance, the availability of basic research on brain effects, and/or the existence of relevant clinical studies (Table 3-1). In this report, we focus on a subset of these factors, which research suggests are implicated in differential developmental outcomes for children by race: premature birth (adequate gestation), fetal alcohol and nicotine exposure, and micronutrient deficiency, and exposure to lead. We do not suggest that these factors are uniquely important to healthy development. Other critical factors, such as the role of iodine in cognitive development, are not considered here because in this country they are unlikely to contribute to current developmental differences, since effective prevention measures have eliminated the iodine deficiency problem for children of all races (Stanbury, 1998).

In each year in the past decade, between 7 and 8 percent of babies were born at weights below 2,500 grams. The vast majority of low-birthweight