This paper reviews and interprets the evidence from 223 rigorous impact evaluations of educational initiatives conducted in 56 low- and middle-income countries. The authors consider for inclusion in their review all studies in recent syntheses, which have reached seemingly conflicting conclusions about which interventions improve educational outcomes. They group interventions based on their theory of action. They derive four lessons from the studies we review. First, reducing the costs of going to school and expanding schooling options increase attendance and attainment, but do not consistently increase student achievement. Second, providing information about school quality, developmentally appropriate parenting practices, and the economic returns to schooling affects the actions of parents and the achievement of children and adolescents. Third, more or better resources improve student achievement only if they result in changes in children’s daily experiences at school. Finally, well-designed incentives increase teacher effort and student achievement from very low levels, but low-skilled teachers need specific guidance to reach minimally acceptable levels of instruction.