Although family–school engagement is important across child and adolescent development, most research, programs, and policies have focused primarily on elementary students and contexts. The current study extends beyond elementary settings by exploring the unique and shared contributions of developmental context on family–school engagement (i.e., across and within elementary- and middle-school settings). Data were drawn from two randomized controlled trials that evaluated the efficacy of teacher training in universal classroom-management practices. Participants included 3,174 students and 207 teachers across 21 elementary and middle schools in the Midwest. Using hierarchical linear modeling, results revealed that family–school engagement was significantly higher in elementary than in middle schools. Student-level characteristics (i.e., identifying as White, participation in the free/reduced-price lunch program, and having lower levels of disruptive behavior) were also associated with higher levels of family–school engagement. In addition, student characteristics (i.e., race/ethnicity and level of disruptive behavior) moderated the relations between family–school engagement and developmental context. Regardless of developmental context, family–school engagement predicted positive end-of-year behavioral outcomes (i.e., increases in youth prosocial skills and decreases in youth concentration problems, disruptive behaviors, and emotional dysregulation). Last, moderation analyses revealed that these effects of family–school engagement were especially pronounced in middle school for concentration problems and emotional dysregulation. Overall, findings provide further support for the value of family–school engagement across development in fostering positive youth outcomes. However, it is evident that more steps must be taken to ensure family–school engagement practices are developed to support the unique needs of middle-school students and contexts.