Spaced repetition: how to study so the material actually sticks
Spaced repetition means going over the same material not once for a long time, but several times for shorter sessions with gaps in between – say the next day, after three days, after a week and after two weeks. You then remember it far longer than after the same amount of time spent cramming. It is one of the best-supported findings in the psychology of learning, and it works even better when each review is a self-test rather than a reread. Oddly, most people underrate it, because last-minute cramming feels more effective.
- A review of hundreds of experiments confirmed that learning spread over time is remembered better than the same learning crammed together (Cepeda et al., 2006).
- The longer you need to remember something, the longer the gaps that pay off (Cepeda et al., 2008).
- With flashcards, spacing beat massing for 90% of participants, yet 72% of them believed the opposite (Kornell, 2009).
- Reviewing by recalling from memory beats rereading for long-term retention (Roediger & Karpicke, 2006).
- In practice: learn once, then review after 1, 3, 7 and 14 days, always by testing, and adjust the gaps to your exam date.
What spaced repetition is
Picture two students. One studies vocabulary for an hour straight the night before a test. The other splits the same hour into four fifteen-minute sessions over the week. The day after the test, both remember about the same. A month later, the second remembers far more. That’s the spacing effect.
Nicholas Cepeda and colleagues (2006) pooled hundreds of experiments on learning words, facts and texts, and the result was consistent: spaced learning leads to better long-term memory than massed learning. The usual explanation is that each review after a little forgetting forces your brain to retrieve the information again – and that retrieval is what strengthens memory.
Why almost nobody uses it
Nate Kornell (2009) had students learn word pairs from flashcards either massed or spaced. Spacing worked better for 90% of the participants. Even so, after the first session, 72% of them believed massing had been more effective.
Why? When you repeat material back to back, it feels familiar, so you think you know it. With spaced review you forget a bit and have to work for it – which feels like failure. In reality, that’s the useful effort. If a review feels suspiciously easy, your gap is probably too short.
How to use spaced repetition
- Learn the material once. Go through a topic or chapter and test yourself without notes at the end. Mark what you don’t know.
- Review the next day. Briefly and from memory: write down what you remember or answer your own questions. Then check.
- Review after three days. Again by testing. Topics that come easily can move to a longer gap next time.
- Review after a week. Give the most time to what still doesn’t stick.
- Review after two weeks, then as needed. If you need it for longer, continue after a month.
- Fit the gaps to your deadline. Cepeda and colleagues (2008) found that the longer you need to remember something, the longer the gaps that pay off: for a test in a week, reviews after one or two days are enough; for an exam months away, gaps of weeks work better.
How to put spacing and self-testing into an exam timetable is covered in how to study for exams.
Review by testing, not rereading
Spaced repetition is strongest when combined with active recall. Henry Roediger and Jeffrey Karpicke (2006) showed that students who read a text once and then tested themselves on it remembered it better a week later than those who reread it repeatedly – even though five minutes after studying it looked the other way round.
Ways to test yourself:
- Flashcards (paper or in an app): a question on one side, the answer on the other. Put the cards you know aside for a longer gap.
- A blank page: write down everything you remember about a topic, then compare with your notes.
- Your own questions: after each block, write three questions to answer next time.
- Explain it out loud: as if you were teaching someone else.
How to fit reviews into a whole exam season is covered in how to make a study schedule.
Where spaced repetition has limits
- It needs time. If the exam is tomorrow, there’s nothing to spread out. Spaced review is an investment that pays back over days and weeks.
- It doesn’t replace understanding. Review what you understand. Understand first, then repeat.
- It’s best studied for facts and vocabulary. For complex skills (solving problems, writing), spaced practice also helps, but there is less research.
Try it now in CORTEX
CORTEX (free for everyone) doesn’t have its own flashcards, but it schedules your reviews: with Capture a thought you type “Review topic 3 tomorrow”, “in 3 days” and “next week”, and the tasks appear on the right days. The “Exam season” template creates reviews 14, 7, 3 and 1 day before an exam by itself. And you can see spaced repetition at work in the Brain Academy: questions from the lessons come back in Review at growing intervals, and what you’ve mastered stops showing. If you have an account, open Review in the Academy.
Frequently asked questions
What is spaced repetition?
Spaced repetition is a way of studying where you go over the same material several times with growing gaps – for example after 1, 3, 7 and 14 days – instead of in one long session. You then remember it much longer.
What are the best intervals?
It depends on how long you need to remember the material. For a test in a week, reviews after one or two days are enough; for an exam months away, gaps of weeks pay off. 1, 3, 7 and 14 days is a reasonable start.
Does spaced repetition work at the last minute?
Only to a limited extent. If the exam is tomorrow, there’s nothing to spread out. The benefit shows over days and weeks, so it’s best to start at least two weeks before the exam.
Should I review by rereading or by testing?
By testing. Research shows that recalling from memory strengthens it more than rereading, even though rereading feels more reassuring. The best combination is gaps plus testing.
Do I need a flashcard app?
No. Paper flashcards sorted into boxes by how well you know them work, or your own questions in a notebook. An app just keeps track of the review dates for you.
Sources and further reading
- Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T. & Rohrer, D. (2006): Distributed practice in verbal recall tasks: A review and quantitative synthesis – Psychological Bulletin
- Cepeda, N. J., Vul, E., Rohrer, D., Wixted, J. T. & Pashler, H. (2008): Spacing effects in learning: A temporal ridgeline of optimal retention – Psychological Science
- Kornell, N. (2009): Optimising learning using flashcards: Spacing is more effective than cramming – Applied Cognitive Psychology
- Roediger, H. L. & Karpicke, J. D. (2006): Test-enhanced learning: Taking memory tests improves long-term retention – Psychological Science
- Dunlosky, J., Rawson, K. A., Marsh, E. J., Nathan, M. J. & Willingham, D. T. (2013): Improving students’ learning with effective learning techniques – Psychological Science in the Public Interest
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