A major decision that must be made during study pertains to the distribution, or the scheduling, of study. In this paper, we review the literature on the benefits of "spacing," or spreading one's study sessions relatively far apart in time, as compared to "massing," where study is crammed into one long session without breaks. The results from laboratory research provide strong evidence for this pervasive "spacing effect" especially for long-term retention. The metacognitive literature on spacing, however, suggests that massing is the preferred strategy, particularly in young children. Reasons for why this is so are discussed as well as a few recommendations regarding how spacing strategies might be encouraged in real-world learning. While further research and applicability questions remain, the two fields--education and cognitive science--have made huge progress in recent years, resulting in promising new learning developments.