Most students study the way they were never taught to: one long session, close to the deadline, with the notes read over and over until they feel familiar. It feels productive. It is also one of the least efficient ways to learn anything you want to remember next month.
The oldest finding in memory research
In the 1880s, the German psychologist Hermann Ebbinghaus memorized lists of nonsense syllables and tested himself at different intervals. Two things stood out. Forgetting is steep at first, then slows down. And a memory that has been revisited fades more slowly than one that has not.
More than a century of experiments since then has confirmed a robust pattern called the spacing effect: the same amount of study, spread over several sessions, produces better long-term memory than the same amount packed into one.1 It holds for vocabulary, for facts, for mathematics and for motor skills, and it holds for children and adults.
Why cramming feels so convincing
Cramming works, for a day or two. If the exam is tomorrow, the material is fresh and recall is easy. That success is the trap. It teaches you that the method works, and by next week most of it is gone.
A classic experiment shows how misleading the feeling can be. Students read a passage and then either re-read it or practised recalling it. Re-reading felt better and gave higher confidence. But a week later, the students who had tested themselves remembered clearly more.2 Learning that feels easy is often shallow. Learning that takes effort, such as pulling something out of memory just as it is slipping, tends to last. The psychologist Robert Bjork called these desirable difficulties.3
How far apart should the sessions be?
There is no magic number, but there is a useful pattern. The best gap depends on how long you need to remember. In a study of more than a thousand people who were tested at different delays, the ideal gap grew as the test got further away, but shrank as a share of that time.4 For a test a week away, a gap of about a day worked best. For a test a month or two away, a gap of a couple of weeks did. If you want to remember something for months, let weeks go by between reviews.
A schedule that works for most people looks like this:
- Day 0: learn the material, then close the book and write down everything you can remember.
- Day 1 or 2: quiz yourself on it. Check what you missed.
- About a week later: quiz yourself again, mixing in older topics.
- A few weeks later: one more round. The facts you still get right can wait longer next time.
Make the effort count
Spacing works best with retrieval. Re-reading the page is the weakest way to use a review slot. Better options:
- Close the notes and write or say what you remember, then check.
- Use flashcards, and put the cards you get wrong back into the pile sooner.
- Answer past exam questions from memory, not from the answer key.
- Mix topics in one session instead of finishing one before starting the next.
A review of ten popular study techniques rated practice testing and distributed practice as the two with the strongest evidence across ages and subjects, and rated highlighting and re-reading as the weakest.5
For teachers and parents
The practical change is small. Put a short, ungraded quiz at the start of a lesson that covers last week's material, and one that covers last month's. Students will say it feels harder. It is supposed to. The difficulty is the mechanism.
A caution. Spacing is not a substitute for understanding. It makes things you understand stick. If something does not make sense yet, fix that first, then space the practice.
References
- Cepeda NJ, Pashler H, Vul E, Wixted JT, Rohrer D. Distributed practice in verbal recall tasks: a review and quantitative synthesis. Psychol Bull. 2006;132(3):354–380. Find it ↗
- Roediger HL, Karpicke JD. Test-enhanced learning: taking memory tests improves long-term retention. Psychol Sci. 2006;17(3):249–255. Find it ↗
- Bjork RA. Memory and metamemory considerations in the training of human beings. In: Metcalfe J, Shimamura A, eds. Metacognition: Knowing about Knowing. MIT Press; 1994:185–205. Find it ↗
- Cepeda NJ, Vul E, Rohrer D, Wixted JT, Pashler H. Spacing effects in learning: a temporal ridgeline of optimal retention. Psychol Sci. 2008;19(11):1095–1102. Find it ↗
- Dunlosky J, Rawson KA, Marsh EJ, Nathan MJ, Willingham DT. Improving students’ learning with effective learning techniques. Psychol Sci Public Interest. 2013;14(1):4–58. Find it ↗