Starting from observed gender differences in educational effort and because research considers motivation to be a personal student feature, this study had two aims. First, it examined whether autonomous and controlled motivation are shared by students within a school and whether such a motivation culture is associated with the school's student composition. Second, the study examined whether students', and specifically boys', class engagement and disruptive behaviour are associated with the motivation culture in their school. The main findings of analyses of data from 5162 eighth-grade students (average age 14) in 57 Flemish secondary schools are that (1) schools are characterized by an autonomous and controlled motivated culture that is related to schools' sex and migrant composition and schools' socioeconomic composition, respectively, and (2) boys' disruptive behaviour is related to the autonomous motivation culture, showing boys are more susceptible to their peers' motivation culture. Implications for research and practice are discussed.