Spaced Repetition

What is spaced repetition?

Spaced repetition is a study technique in which you revisit a piece of information not once, but repeatedly over days, weeks and months, with the gap between reviews growing each time. Instead of ten repetitions in a single evening, you spread them across several sessions. The method rests on two robust memory findings: the spacing effect (distributed study beats massed study) and the testing effect (actively retrieving information strengthens memory more than rereading it).

Why does spaced repetition work?

After you learn something, the memory trace decays quickly at first – a pattern captured by the Ebbinghaus forgetting curve. Reviewing the material just as it begins to fade re-consolidates the trace and flattens the decline, so each successive review buys a longer period of retention. The large meta-analysis by Cepeda and colleagues (2006), covering 317 experiments, confirmed that distributed practice reliably improves later recall, and that the ideal gap grows with how long you need to remember. Dunlosky and colleagues (2013) rated distributed practice among the most effective of ten common study strategies.

How do you apply spaced repetition?

The classic tool is flashcards organised with the Leitner system: cards you answer correctly move into boxes reviewed less often, while mistakes send a card back to short intervals. Software such as Anki or SuperMemo automates this scheduling, computing an individual next-review date for every card. What matters is that each review is a genuine retrieval attempt – answer first, then check. Spaced repetition is especially valuable for large bodies of factual material such as vocabulary, anatomy or law, because it concentrates limited study time on exactly the items that are currently at risk of being forgotten.

One caveat: spacing makes each session feel harder and less fluent than cramming, which can mislead learners into abandoning it. That extra effort — a so-called desirable difficulty — is precisely what drives the long-term gain, and it holds across ages, subjects and time scales. Spaced repetition does not replace understanding; it schedules the review of material you have already made sense of.