The eleven studies which comprise the Consortium for Longitudinal Studies were described in order to determine long-term effects of preschool education on disadvantaged children. Research methods and results of the studies were evaluated and compared. An historical overview details the sociopolitical milieu from the time the eleven studies began in the 1960s to the present. Theories which impacted the preschool movement in the 1960s were also discussed, particularly those which concern the development of intelligence, the importance of early education and environmental impact on the development of intelligence. Demographic data were used to describe disadvantaged children's needs for quality early intervention programs. The results of the eleven Consortium studies indicate positive long-term effects for disadvantaged children enrolled in quality preschool programs.