Multiple meta-analyses have now documented small positive effects of teacher professional development (PD) on pupil test scores. However, the field lacks any validated explanatory account of what differentiates more from less effective in-service training. As a result, researchers have little in the way of advice for those tasked with designing or…

Teachers have an important influence on pupils' academic progress, yet the quality of teaching varies widely. Policymakers, school leaders, and teacher educators therefore face the challenge of designing and commissioning professional development (PD) to help all their teachers become as effective as the best teachers. In the last two decades, a…