Publicly-funded, center-based, comprehensive early childhood development programs for low income children aged 3 to 5 years are recommended based on strong evidence of their effectiveness on preventing delay of cognitive development and increasing readiness to learn, as assessed by reductions in grade retention and placement in special education classes. There was insufficient evidence to determine the effectiveness of early childhood development programs on social cognition and social risk behaviors because findings were limited to the longitudinal results of a single program. Evidence was also insufficient to determine the effectiveness of early childhood programs on child health screening outcomes and family outcomes because of a lack of sufficient comparative studies examining these outcomes. Comprehensive, center-based early childhood development programs are defined as publicly funded comprehensive preschool programs designed to improve the cognitive and social development of children, aged 3 to 5 years, at risk because of family poverty.