BACKGROUND Internalizing problems have increased among Swedish adolescents. We examined whether classroom disorder was associated with internalizing problems and whether it explained the trends in internalizing problems. Furthermore, we examined whether school contextual factors were associated with internalizing problems and whether they moderated the association between classroom disorder and internalizing problems. METHODS We used repeated cross-sectional survey data (1988-2011) among all 15- to 16-year-old students in Varmland, Sweden (N = 9491 boys, N = 9313 girls). School-level factors were the proportions of students with a low/average socioeconomic or an immigration background. RESULTS Results from mixed effects models showed that classroom disorder was associated with internalizing problems across the years of investigation but did not explain the trends in internalizing problems. This association was moderated by the school-level proportion of students with a low/average socioeconomic background but not the school-level proportion of students with an immigration background. CONCLUSIONS Students who perceived their classroom to be disorderly more often also reported more internalizing problems. Future studies are necessary to investigate other potential school factors that may explain the trends in internalizing problems.