This study explored the role of clique membership and clique isolation in children's psychosocial adjustment. We identified change and stability in early elementary school clique membership and investigated behavioral characteristics related to this change and stability. Participants were first-grade pupils (N = 300), followed over a 1-year period. Clique membership was identified through social network analysis. Differences between children with a stable versus changing clique membership status were tested using peer nominations and teacher ratings. Clique members were better adjusted than nonclique members. Externalizing behavior, less prosocial behavior, and low social preference preceded clique estrangement. Stable-isolates increased in externalizing behavior, whereas children who became part of a dyad or included in a clique showed a decrease in externalizing behavior. (Contains 5 tables.)