Evidence points to associations between the socioeconomic composition of neighborhoods and children's and adolescents' development. A minimal amount of research, however, examines how timing of exposure to neighborhood socioeconomic conditions matters. This study used longitudinal data from the NICHD Study of Early Child Care and Youth Development (N = 1,364) to explore if timing of exposure (early childhood, adolescence, and cumulative) to neighborhood affluence and poverty had differential associations with children's achievement and behavior problems concurrently and in adolescence. Results indicate that children in neighborhoods with more affluent residents during early childhood had higher achievement and fewer internalizing behaviors contemporaneously and that these associations endured until adolescence for reading achievement. Long-term exposure to affluent neighborhoods was associated with children's math and reading achievement in adolescence. Findings are discussed in terms of research and policy implications.