["Psychology in the Schools, EarlyView. ", "\nABSTRACT\nReducing teacher burnout and improving student behavior are national challenges. This study reports on a randomized controlled trial testing effectiveness of a telementoring professional development (PD) model, called ECHO, to build teachers' capacity to promote their students' prosocial behavior while supporting their own well‐being. The sample included 109 middle school teachers (59 intervention, 50 waitlist control) and their 1091 students. The intervention included eight telementoring sessions over a school year. Intervention teachers reported significantly less burnout and intent to leave the profession, greater self‐efficacy for managing peer relations, and their students reported greater feelings of belonging compared to the control group. Given its low cost and scalability, the telementoring ECHO model is a promising approach for teacher professional development."]