This research examined whether 5th-grade students' (N = 602) perceptions of the classroom social environment (teacher support, promotion of mutual respect, promotion of task-related interaction, student support) were related to their engagement in the classroom (self-regulation and task-related interaction) and whether those relations were mediated by personal motivational beliefs (mastery goals, academic and social efficacy). Teacher support, promotion of interaction, and student support were related to both types of engagement, and those relations were fully or partially mediated by motivational beliefs. Relations with promoting mutual respect were not significant.