This document reviews the findings of relatively small, controlled, long-term evaluations of preschool programs in various parts of the country. It is an attempt to clarify unresolved issues arising from the Westinghouse Learning Corporation Report on the impact of Project Head Start. Generally, this review focuses on the following question: What is known about the impact of any type of preschool intervention program? The report includes chapters on (1) Head Start graduates in school (studies from New Haven, Connecticut), (2) impact of early education on disadvantaged children (based on a Philadelphia study), (3) a five-year enrichment curriculum ranging from preschool to third grade levels (New York City, IDS Program), (4) the Early Training Project, (5) effects of economic deprivation on nursery school performance (study at Howard University), (6) The Karnes' Preschool Program (University of Illinois, Urbana-Champaign), (7) The Learning to Learn Program, and (8) The Ypsilanti Perry Preschool Project. It is concluded that early intervention does have an immediate impact (within one year) on the child's performance when measured by the Stanford-Binet, or personal-social adjustment ratings. On a long term basis, positive impact of intervention programs on school performance has been reported. Variables such as age, sex, and socio-economic status may affect the quality of intervention impact. (DP)