Helping teachers become more effective in the classroom is a high priority for school leaders and policymakers. This study examined one promising strategy for improving teachers' effectiveness: providing individualized coaching using videos of teachers' instruction for reflection, practice, and feedback. The coaching focused on general, rather than subject specific, teaching practices. About 100 elementary schools were randomly divided into three groups: one where teachers received five highly structured cycles of focused, professional coaching during a single school year, one where teachers received more coaching (eight cycles), and one that continued with its usual strategies for supporting teachers. The study compared teachers' experiences and their students' achievement across the three groups to determine the effectiveness of the two versions of the coaching.