participating in Early Head Start scored significantly higher than those not participating on the Mental Development Index of the Bayley Scales of Infant Development, and fewer of them were in the “at risk” category on this index. They had significantly larger vocabularies, significantly lower levels of aggressive behavior, higher levels of sustained attention, greater engagement with parents, and less negativity toward parents. Program impact was generally larger among families that enrolled during pregnancy, African American families, and those with a moderate number of risk factors. Families with four or five of the following risk factors did not benefit: no high school education, single parent, teen parent, receiving public assistance, and not employed or in school. Two years after program completion, some of the program benefits had dissipated (positive effects on aggressive behavior or negativity during play were not sustained), and additional benefits emerged (including enrollment in formal education programs and positive interactions in the home).

Preschool education has been shown to have positive effects on the language skills, literacy, and general cognitive ability of young children in several evaluations of high-quality programs (Yoshikawa, Schindler, and Caronongen, 2007). Two meta-analyses report overall positive outcomes of preschool programs. In a review of 13 evaluations of state-funded preschool programs for children ages 3-5, Gilliam and Zigler (2001) report improved developmental competence. Although significant impact was limited to kindergarten and first grade, some effects, including increased later school attendance and decreased grade retention, were sustained for several years. Only four of the evaluations assessed behavior problems; one of these showed a significant long-term effect through fourth grade.

A second meta-analysis (Nelson, Westhues, and MacLeod, 2003) of universal and indicated (high-risk) preschool prevention programs—many of which included home visiting, parent training, or preschool education components—found significant program effects on children’s cognitive functioning (when assessed during preschool years), children’s social-emotional functioning (during elementary school), and family functioning (during elementary school). Effects on social-emotional functioning were sustained even after children had finished high school.

Programs that provided preschool education had significantly greater effects on children’s cognitive development than those that did not. Preschool children continued to do better in elementary school, but the differences were not significant. Programs with more child and family contact also had significantly greater impact on both cognitive functioning during