Hierarchical linear modeling is used to assess individual student, family, and school predictors of aggression in 111,662 students in sixth, seventh, and eighth grades. Nine measures of problem-solving strategies, quality of family and peer interaction, and perceptions of school climate are analyzed at the individual student level. Eight measures of school climate are included in the analysis at the school level. Aggression is operationalized with student self-report of the previous 6-month frequency of hitting others, being mean to others, and getting into a fight. At the level of the individual student, measures of problem solving were most strongly predictive of aggression. Inclusion of students in policy and rule processes, cultural sensitivity education, and teaching that emphasizes understanding over memorization were significant predictors of aggression at the school level. The potential for abatement of student aggression across individual and school levels offers opportunities for further testing of interventions for the child and the school. (Contains 2 tables.)