This study capitalizes on recent advances in the reliable and valid measurement of classroom-level social processes known to influence children's social-emotional and academic development and addresses a number of limitations in our current understanding of teacher- and intervention-related impacts on elementary school classroom processes. A cluster randomized controlled trial design was employed to (a) examine whether teacher social-emotional functioning forecasts differences in the quality of 3rd-grade classrooms, (b) test the experimental impact of a school-based social-emotional learning and literacy intervention on the quality of classroom processes controlling for teacher social-emotional functioning, and (c) examine whether intervention impacts on classroom quality are moderated by these teacher-related factors. Results indicated (a) positive effects of teachers' perceived emotional ability on classroom quality; (b) positive effects of the 4Rs Program on overall classroom quality, net of teacher social-emotional functioning indicators; and (c) intervention effects that are robust to differences in these teacher factors. These findings support and extend recent research examining intervention-induced changes in classroom-level social processes fundamental to positive youth development.