The purpose of this workshop is to train researchers and evaluators how to plan efficient and effective cluster and multisite randomized studies that probe hypotheses concerning main effects, mediation, and moderation. We focus on the conceptual logic and mechanics of multilevel studies and train participants in how to plan cluster and multisite randomized studies with adequate power to detect multilevel mediation, moderation, and main effects. We introduce participants to the free PowerUp! software programs designed to estimate the statistical power to detect mediation, moderation, and main effects across a wide range of designs. The workshop will combine lecture with hands-on practice with the free software programs. The target audience includes researchers and evaluators interested in planning and conducting multilevel studies that investigate mediation, moderation, or main effects. Participants should bring a laptop to the session.