Increasing Retention Without Increasing Study Time

Because people forget much of what they learn, students could benefit from learning strategies that yield long-lasting knowledge. Yet surprisingly little is known about how long-term retention is most efficiently achieved. Here we examine how retention is affected by two variables: the duration of a study session and the temporal distribution of study time across multiple sessions. Our results suggest that a single session devoted to the study of some material should continue long enough to ensure that mastery is achieved but that immediate further study of the same material is an inefficient use of time. Our data also show that the benefit of distributing a fixed amount of study time across two study sessions—the spacing effect—depends jointly on the interval between study sessions and the interval between study and test. We discuss the practical implications of both findings, especially in regard to mathematics learning. KEYWORDS—spacing; overlearning; education; learning; mathematics Although most people have spent thousands of hours in the classroom, the result of this effort is often surprisingly disappointing. Indeed, both the popular press and the academic literature are replete with examples of educational failure among students and recent graduates. In one assessment of U.S. eighth graders, only 50% were able to correctly multiply 5 and 7 (Reese, Miller, Mazzeo, & Dossey, 1997), and a recent survey of young adults in the United States revealed that most could not identify the continent in which Sudan is located (National Geographic, 2006). While such findings are partly explained by the fact that some students never learned the information in the first place, we believe that forgetting is often the cause. For this reason, it seems important to define learning strategies that can promote long-lasting retention. Yet surprisingly little is known about the long-term effectiveness of most learning strategies. We have been conducting learning experiments in which subjects are tested as much as 1 year after the final study session. In a further nod to ecological validity, our subjects learn the kinds of material that people often try to learn, such as vocabulary, geography, foreign languages, and mathematics (e.g., Pashler, Rohrer, Cepeda, & Carpenter, 2007). In this review, we focus on two decisions that all learners face: How long should one study the same material before quitting or shifting to different material, and how should a fixed amount of study time be distributed across study sessions?