We estimate the direct and spillover effects of a large-scale early childhood intervention on the educational attainment of over 2,000 disadvantaged children in the United States. We show that failing to account for spillover effects results in a severe underestimation of the impact. The...

We randomly assign more than 6,000 students from 150 primary schools in Bangladesh to work on math assignments in one of three settings: individually, in groups with random schoolmates, or in groups with friends. The groups consist of four people and are balanced by average cognitive ability and...