Background/Context: When a researcher tests an educational program, product, or policy in a randomized controlled trial (RCT) and detects a significant effect on an outcome, the intervention is usually classified as something that "works." When the expected effects are not found, however, there is seldom an orderly and transparent…

This report examines theoretical and empirical issues related to the statistical power of impact estimates under clustered regression discontinuity (RD) designs. The theory is grounded in the causal inference and HLM modeling literature, and the empirical work focuses on commonly-used designs in education research to test intervention effects on…