Abstract: Learners forget much of what they learn in school, even in as short a time as a summer vacation. Many educational lapses reflect failure to retain, rather than failure to understand. We present the work of our IES-supported team -- including Rohrer, Cepeda, Wixted, and Carpenter, as well as the presenter--seeking to identify factors that can reduce the rate of forgetting and increase the efficiency of learning. One issue described in detail is the role of temporal spacing of learning. Previous studies have characterized spacing effects over short time intervals, but we present new results examining temporal spacing effects over retention intervals of up to one year. These studies hold the amount of study time constant, and look at how the temporal distribution of study periods affects the rate of forgetting after the final session. The results show that spacing of study has powerful effects, with optimal spacing of approximately 10-20% of the retention interval. Optimal spacing can increase the amount of information retained after a long delay by a factor of two or three. Our findings imply that whenever the goal of education is to produce memory that will endure for years, it is enormously useful to spread the learning out over a relatively long period of time (e.g., one year).