This study used longitudinal data from the Infant Health and Development Program (IHDP) to examine three issues regarding effects of economic deprivation on child development: (1) the effects on children's developmental outcomes of poverty and such poverty correlates as single parenthood, ethnicity, and maternal education; (2) the developmental consequences of the duration and timing of family economic deprivation; and (3) the comparative influence of economic deprivation at the family and neighborhood level. The IHDP was an eight-site clinical trial that tested the efficacy of educational and family-support services and high quality pediatric follow-up in the first 3 years of life in reducing the incidence of developmental delay in low-birthweight, preterm infants. Analysis of data showed that family income and poverty status were powerful correlates of children's cognitive development and behavior. Although the duration of poverty was a significant factor, its timing in early childhood was not. Five-year-olds' IQs were higher in neighborhoods with greater concentrations of affluent neighbors, while the prevalence of low-income neighbors appeared to increase the incidence of externalizing behavior problems. (Contains 104 references.) (MM)