This longitudinal study examined trajectories of change in adolescents' perceptions of four dimensions of school climate (academic support, behavior management, teacher social support, and peer social support) and the effects of such trajectories on adolescent problem behaviors. We also tested whether school climate moderated the associations between deviant peer affiliation and adolescent problem behaviors. The 1,030 participating adolescents from eight schools were followed from sixth through eighth grades (54% female; 76% European American). Findings indicated that all the dimensions of school climate declined, and behavioral problems and deviant peer affiliation increased. Declines in each dimension were associated with increases in behavioral problems. The prediction of problem behavior from peer affiliation was moderated by adolescents' perceptions of school climate.