Sixteen middle schools were recruited for participation in the School Social Environments study, a 3-year longitudinal study of student friendships and behavior. Schools were located in the western United States, and were chosen for recruitment based on a target enrollment range of 100 to 1,000 students and availability of school resources for conducting supervised, web-based surveys. Of the schools recruited, 14 participated in at least 1 year of the study. Eleven schools enrolled grades 6, 7, and 8; two schools enrolled only grades 7 and 8; and one school enrolled grades 6 through 12. The present study excluded the grade 6–12 school because of the uncertain effect of older adolescents on the same campus, and one other school that did not complete four assessments in one year. Enrollments in the remaining 12 schools included in this analysis varied from approximately 120 to 600 students, varying slightly by assessment wave. All students enrolled at any time during their school’s 3-year participation were eligible to participate. All schools were exposed to the school-wide Positive Behavioral Intervention and Support program (PBIS; Horner et
