This study examined the effects of behavioral and social engagement and classroom supportiveness on the development of civic efficacy in fourth-grade science classrooms. We define civic efficacy as children's beliefs that they are not only capable of making a difference in their community, but they also feel a responsibility to do so. This study enrolled 815 students (48% female) across 39 classrooms, including 31 fourth-grade teachers at 25 schools in a large urban school district in the South Central U.S. Stepwise regression showed that behavioral engagement, social engagement, and classroom supportiveness in science class all positively predicted civic efficacy, and social engagement accounted for the greatest amount of variance in that civic efficacy. Findings suggests that social engagement is a stronger driver of civic efficacy than behavioral engagement and classroom supportiveness, pointing to the importance of collaboration and teamwork in science classrooms. We discuss implications for elementary classroom practices.