Neighborhoods are an important social context for children’s development; however, a growing body of research illustrates that there is often significant heterogeneity in how neighborhoods influence children’s outcomes. Scholars have therefore focused greater attention on understanding neighborhood effect heterogeneity and the social processes that underpin this variation. Recent quantitative work has pointed to heterogeneity by age in the effects of moving to low-poverty neighborhoods, but questions remain about the mechanisms that explain why youth of different ages have divergent outcomes after this move. This paper examines the social processes that drive differences in neighborhood effects by age through analysis of qualitative interviews with low-income Black youth who moved to lower-poverty and more racially integrated neighborhoods with a housing mobility program. The findings show that the process of friendship formation serves as an important mechanism for age differences in school engagement after moving to non-poor neighborhoods. Adolescents in this sample hesitated to form new friendships after moving, choosing a strategically cautious approach to engaging with new peers. In contrast, youth who moved during middle childhood quickly formed friendships in their new communities. These new friends then encouraged children’s engagement and motivation in their new schools, amplifying the potential for children to experience positive educational effects following this move. Younger youth experienced the dual advantages of less exposure to high-poverty neighborhoods and an easier process of establishing new friendships in their suburban communities.