The goal of this research is to examine the trajectory of school bonding over the middle school period and how factors such as gender, substance use, antisocial peers, delinquent behavior, and academic achievement affect this developmental process. Data from four waves of measurement of 2,902 adolescents are analyzed using hierarchical growth curve modeling. Results suggest that school bonding decreases in a nonlinear fashion from Grades 6 to 8. However, school bonding development varies based on interindividual differences. Boys have lower initial levels and greater decreases in school bonding than girls. Student deviant behavior, having antisocial peers, and low academic achievement are associated with lower levels of school bonding at Grade 6. Low grades and an increase in substance use are associated with a steeper decrease of school bonding over time. Increases in substance use and being male are also associated with a curvilinear pattern of school bonding. Implications for interventions are discussed. (Contains 1 figure and 5 tables.)