Lessons Learned from Large-Scale Randomized Experiments

Large-scale randomized studies provide the best means of evaluating practical, replicable approaches to improving educational outcomes. This article discusses the advantages, problems, and pitfalls of these evaluations, focusing on alternative methods of randomization, recruitment, ensuring high-quality implementation, dealing with attrition, and data analysis. It also discusses means of increasing the chances that large randomized experiments will find positive effects, and interpreting effect sizes.