Student behavioral engagement is a key condition supporting academic achievement, yet student disengagement in middle and high schools is all too common. The current study used a randomized controlled design to test the efficacy of the My Teaching Partner-Secondary program to increase behavioral engagement. The program offers teachers personalized coaching and systematic feedback on teachers' interactions with students, based on systematic observation of videorecordings of teacher-student interactions in the classroom. The study found that intervention teachers had significantly higher increases, albeit to a modest degree, in student behavioral engagement in their classrooms after 1 year of involvement with the program compared to the teachers in the control group (explaining 4% of variance). In exploratory analyses, two dimensions of teachers' interactions with students--their focus on analysis and problem solving during instruction and their use of diverse instructional learning formats--acted as mediators of increased student engagement. The findings offer implications for new directions in teacher professional development and for understanding the classroom as a setting for adolescent development.