Although findings on the positive effects of early childhood development programs have been widely disseminated, less attention has been given to program impacts across the entire period of early childhood. This review summarizes evidence on the effects and cost-effectiveness of programs and services from ages 3 to 9. The major focus is preschool programs for 3- and 4-year-olds, full-day kindergarten, school-age programs including reduced class sizes, and preschool-to-third-grade interventions. Participation in preschool programs was found to have relatively large and enduring effects on school achievement and child well-being. High-quality programs for children at risk produce strong economic returns ranging from about $4 per dollar invested to over $10 per dollar invested. Relative to half-day kindergarten, the positive effects of full-day kindergarten have been found to be relatively small and generally do not last for more than a year. Although no formal economic analyses have been conducted, the economic return per dollar invested would be expected to be close to zero. Among early-school-age programs, preschool plus school-age interventions (PK-3) for children at risk are linked to higher levels of school performance into adolescence. The Child-Parent Center PK-3 Program shows a return of $6 to $9 per dollar invested. Class-size reductions show evidence of positive effects, with economic returns of roughly $3 per dollar invested. The causal mechanisms of long-term effects are discussed. Key principles to promote intervention effectiveness are offered.