This article examines the influence of personal background characteristics, family involvement, and ability grouping on school commitment, which, in turn, affects the extent of students' participation in school crime, school misconduct, and school nonattendance. Observational and survey data from a sample of 754 middle school students in Grades 7 and 8 support the hypothesis that decreasing levels of school commitment are linked to increasing rates of school crime, school misconduct, and school nonattendance. Personal background, family involvement, and ability grouping help to explain the level of school commitment. Higher school commitment is associated with being female, White, in the eighth grade, and in high-ability mathematics classes. Youths with more educated mothers and youths whose parents are highly involved in their schooling are also more educationally committed. School commitment mediates much of the effects of personal background, family involvement, and ability grouping on the school delinquency measures. These findings can serve as a basis for early school-based delinquency prevention efforts.