This study examined longitudinal associations between early adolescents' school friendship stability, instability, and network size and their perceived social adjustment. The final sample consisted of 430 early adolescents residing in seven Midwestern schools (52% female, 47% Black, 42% White, 5% Hispanic or Latinx, and 6% Other). School friendship stability, instability, and network size were assessed via students' peer nominations of their same-grade friendships collected midway through their 7th and 8th grade years. Students also self-reported on several measures of social adjustment (their social satisfaction, social confidence, and school belonging). Results indicated having new friendships and having a larger friendship network at school were each more predictive of early adolescents' perceived social adjustment than was having maintained friendships or a consistent friend group within this context. However, school friendship stability consistently predicted greater perceived school belonging, whereas having a primarily new friend group and/or having lost more or most of a prior friend group predicted lower levels of this perception. Having lost school friendships was not predictive of early adolescents' social adjustment except when losses composed a significant proportion of their school friendship network (i.e., they had lost more or most of their school friendships from the year before). These findings provide valuable insights about peer friendship dynamics and social adjustment during a life stage critical to social development.