Including all Head Start research (both published and unpublished) and using, when possible, the statistical technique of meta-analysis, this final report of the Head Start Evaluation, Synthesis, and Utilization Project presents findings on the impact of Head Start on children's cognitive and socioemotional development, on child health and health institutions in the community, on enrollees' families, and on communities where Head Start programs operate. The report concludes that children enrolled in Head Start enjoy significant immediate gains in cognitive test scores, socioemotional test scores, and health status. In the long run, cognitive and socioemotional test scores of former Head Start students do not remain superior to those of disadvantaged children who did not attend Head Start. However, a small subset of studies find that former Head Starters are more likely to be promoted to the next grade and are less likely to be assigned to special education classes. Head Start also has aided families by providing health and social and educational services and by linking families with services available in the community. Finally, educational, economic, health care, social service, and other institutions have been influenced by Head Start staff and parents to provide benefits to both Head Start and non-Head Start families in their respective communities. (RH)