Learning and memory are generally improved by repetition. However, not all repetitions are equally beneficial. The effectiveness of repetitions depends in part on their temporal distribution. A piece of information studied on several occasions widely spaced apart in time will be remembered better than a similar fact studied on several occasions close in time.

The advantage of distributed repetitions over spaced repetitions has long been known. Hermann Ebbinghaus discussed distributed practice effects in his classic 1885 monograph on memory. He noted that "with any considerable number of repetitions a suitable distribution of them over a space of time is decidedly more advantageous than the massing of them at a single time" (p. 89). Similarly, Jost (1897) formulated the advantage of distributed over massed repetitions as one of his laws of memory. In subsequent decades, distribution of repetition became an important manipulation in the study of learning and...