School moves during adolescence predict lower peer integration and higher exposure to delinquent peers. Yet mobility and peer problems have several common correlates, so differences in movers' and non-movers' social adjustment may be due to selection rather than causal effects of school moves. Drawing on survey and social network data from a sample of seventh and eighth graders, this study compared the structure and behavioral content of new students' friendship networks with those of not only non-movers but also students about to move schools; the latter should resemble new students in both observed and unobserved ways. The results suggest that the association between school moves and friends' delinquency is due to selection, but the association between school moves and peer integration may not be entirely due to selection.