The degree to which intellectual development can be enhanced by systematic early educational intervention, and the relative power of early versus later intervention as a preventive measure against mild retardation and academic failure, were the central issues tested in the Carolina Abecedarian Project. The project was designed for infants and children from socioeconomically disadvantaged families. It provided interventions at the preschool and primary school levels. A day care center provided direct instruction to infants and children and educational materials to parents. Parents used the materials at home with their children to supplement the primary school curriculum. Participants were 109 families of children who were free of conditions known to have genetic or infectious links to mental retardation and who came from homes with low levels of parental income and education or histories of social maladjustment. Duration and type of intervention were systematically varied. Each high-risk subject was matched with a same-sex child in his or her class. Findings demonstrated that early educational intervention could significantly benefit children at high risk for academic failure. Results suggest that intervention should begin in infancy. Children who appear to benefit most are those of mothers with very low intelligence. A total of 33 references are cited. (RH)