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…

Background/Context: Despite the surge in efficacy studies, a recent meta-analysis indicates that the relative effectiveness of any two math interventions is largely unknown (Nelson & McMaster, 2019). Additionally, policy makers rarely choose educational programs based on an assessment of costs and cost-effectiveness (Hollands et al., 2016;…