The Spacing Effect

In the 1880s, the German psychologist Hermann Ebbinghaus carried out some of the first careful experiments on memory. He used himself as the only subject. To make sure that meaning would not help him remember, he created lists of nonsense syllables, short combinations of letters such as "wid" and "zof" that are not real words. He then studied the lists and measured how quickly he forgot them.

One of his findings has proved especially useful. Ebbinghaus compared two ways of learning the same material. In one, he repeated a list many times in a single session. In the other, he spread his repetitions over several days. The second method needed fewer repetitions in total to reach the same level of memory. This result is now called the spacing effect.

Since Ebbinghaus, hundreds of studies have confirmed the effect with real vocabulary, facts, and skills, and with learners of every age. Researchers are still discussing why it works. One explanation is that a gap allows some forgetting to happen. When a learner returns to the material, they must make an effort to recall it, and that effort appears to strengthen the memory more than easy repetition does.

For students, the lesson is practical. Five hours of study spread across a week are likely to produce longer-lasting memory than the same five hours the night before an exam.