A meta-analytic review of the distribution of practice effect: Now you see it, now you don't

The present review examined the relationship between conditions of massed practice and spaced practice with respect to task performance. A meta-analysis of 63 studies with 112 effect sizes yielded an overall mean weighted effect size of 0.46, indicating that individuals in spaced practice conditions performed significantly higher than those in massed practice conditions. Subsequent analyses, however, suggested that the nature of the task being practiced, the intertrial time interval, and the interaction between these two variables significantly moderated the relationship between practice conditions and performance. In addition, significantly higher effect sizes were found in studies with low methodological rigor as compared with those studies higher in rigor. Directions for future research and applications of the findings are discussed.