The present meta-analysis examines the effect of grade retention on academic outcomes and investigates systemic sources of variability in effect sizes. Using multilevel modeling (MLM), the authors investigate characteristics of 207 effect sizes across 22 studies published between 1990 and 2007 at two levels: the study (between) and individual (within) levels. Design quality is a study-level variable. Individual-level variables are median grade retained and median number of years postretention. Quality of design is associated with less negative effects. Years postretention is negatively associated with retention effects, and this effect is stronger for studies using grade comparisons versus age comparisons. The results challenge the widely held view that retention has a negative impact on achievement. Suggestions for future research are discussed. (Contains 4 tables and 4 notes.)