Spaced repetition: what the research says

The short answer: reviewing material in sessions spread out over time works better than the same amount of review crammed together. This is one of the most reliable findings in memory research. The longer you need to remember something, the longer the gaps between reviews should be.

The spacing effect

Hermann Ebbinghaus described it in the 1880s, and it has been tested thousands of times since. In 2006, Nicholas Cepeda and colleagues combined 839 comparisons from 317 experiments. Spaced practice beat massed practice across the board. They also found that the best gap between study sessions grew with the retention interval, meaning how long after studying you are tested.

How long should the gaps be?

A follow-up study by the same group in 2008 tested more than 1,300 people with gaps of up to several months between sessions and final tests up to a year later. The best gap was not fixed. It was a fraction of how long you need to remember: relatively larger for a test a week away and smaller, as a share, for a test a year away. In practice that means gaps of a day or two for something you need next week, and gaps of weeks for something you want to keep for a year.

Testing yourself makes spacing stronger

In 2013, John Dunlosky and colleagues reviewed ten popular study techniques. Only two earned their highest rating for usefulness: distributed practice (spacing) and practice testing (recalling answers instead of rereading them). Highlighting and rereading came out near the bottom. Flashcards combine both: you test yourself, and a good app spaces the cards out for you.

How to use it for a language

• Use a spaced repetition app for vocabulary. It schedules each word just as you are about to forget it, so you don’t have to plan gaps yourself.
• Recall before you check. Say the word or sentence out loud before you flip the card. Recognising it isn’t the same as remembering it.
• Space your skills too. Return to grammar points, listening topics and speaking situations over weeks instead of doing each once.
• Keep the habit visible. Spacing only works if you keep coming back. A short daily log of what you practised makes gaps and streaks easy to see. More on that in how to keep a language learning diary.

Sources

1. Cepeda NJ, Pashler H, Vul E, Wixted JT, Rohrer D. Distributed practice in verbal recall tasks: a review and quantitative synthesis. Psychological Bulletin 2006;132(3):354–380. PubMed 16719566.
2. Cepeda NJ, Vul E, Rohrer D, Wixted JT, Pashler H. Spacing effects in learning: a temporal ridgeline of optimal retention. Psychological Science 2008;19(11):1095–1102.
3. Dunlosky J, Rawson KA, Marsh EJ, Nathan MJ, Willingham DT. Improving students’ learning with effective learning techniques. Psychological Science in the Public Interest 2013;14(1):4–58.