This article examines changes in the research design, sample size, and precision between the planning phase and implementation phase of group randomized trials (GRTs) funded by the Institute of Education Sciences. Thirty-eight GRTs funded between 2002 and 2006 were examined. Three studies revealed changes in the experimental design. Ten studies showed decreases in the total number of groups randomized, whereas 18 studies showed increases. In five cases, the decreases in the number of groups randomized were large enough to decrease the precision of the study. However, in the majority of the studies, the precision was relatively unchanged from planning phase to implementation phase. The consistency in the precision between the planning phase and implementation phase highlights the importance of planning adequately powered studies.