The short answer
Spaced repetition means reviewing the same material several times with gaps in between, instead of all at once. The best gap depends on when your exam is: the further away it is, the longer the gaps can be. A study of more than 1,350 people found the best gap was roughly 20 to 40% of the time until a test a week away, and 5 to 10% for a test a year away.
Why you forget, and why cramming feels like it works
So you learn something on Monday, you know it on Tuesday, and by the following week it's mostly gone. That isn't a memory problem. That's just how memory works for everyone. What changes how much you keep is when you come back to it.
Cramming feels effective because you test yourself the next morning, while it's all still fresh. But exams in Year 11 and 12 test what you learned weeks or months ago. Cramming is a bit like filling a bucket with a hole in it right before you need the water: it's full when you check, and empty when it counts.
What the research says about the gaps
Spacing your study is one of the most studied effects in learning. A review of 839 results from 317 experiments found that spreading study out beats massing it together, and that the best gap between sessions gets longer as the time until the test gets longer [1].
A later study taught more than 1,350 people a set of facts, gave them a review after a gap of up to three and a half months, and tested them up to a year later [2]. At any test date, a longer gap first helped and then slowly hurt. When the gap is measured as a share of the time until the test, the best gap fell from about 20 to 40% for a test a week away to about 5 to 10% for a test a year away.
A large review of study techniques rated spaced practice (they call it distributed practice) as one of only two techniques with high usefulness. The other was practice testing [3].
How to set your own gaps
Here's how I'd turn that research into a plan you can actually use. Start from your exam date and work backwards:
| Your test is... | Gap between reviews | Where the gap comes from |
|---|---|---|
| 1 week away (a class test) | 1 to 3 days | 20 to 40% of 7 days [2] |
| A term away (about 10 weeks) | About 1 to 2 weeks | Our rule of thumb between the study's two ends |
| A year away (the HSC, VCE or QCE) | About 2 to 5 weeks | 5 to 10% of a year [2] |
The middle row is our own estimate, sitting between the two points the study measured. It isn't a number from the paper. The principle is the part that's well supported: the further away the exam, the longer you can wait between reviews.
A worked revision timetable for a Year 12 term
Say you learn a topic in Week 1 of Term 2 and your trial exams are at the start of Term 3. Here's how to space that one topic:
| When | What you do | Time |
|---|---|---|
| Day 1 (the lesson) | Write your notes, then blurt the main ideas from memory | 20 min |
| Day 2 | Short recall: 5 questions on the topic, closed book | 10 min |
| Week 2 | Blurt the whole topic, check and fix the gaps | 15 min |
| Week 4 | One past-paper question on it, marked against the guidelines | 20 min |
| Week 7 | Flashcards from your gaps, mixed with other topics | 10 min |
| Holidays | One mixed practice paper that includes it | Part of a full paper |
Notice that each review is short, and each one is a recall task, not a re-read. Spacing and recall work best together. Testing yourself is what makes each spaced review count [4].
Making spacing easy to stick to
- Use a flashcard app with spaced scheduling (Anki is free) so it decides what's due each day.
- Or use a paper calendar: when you learn a topic, write its next three review dates in the calendar straight away.
- Keep reviews short. Ten to fifteen minutes is enough. A review you actually do beats a perfect one you skip.
- Mix topics in each review session, rather than reviewing one topic for an hour.
Common mistakes
- Re-reading at each review. Spaced re-reading is better than crammed re-reading, but spaced recall is better again.
- Starting too late. If the exam is in a week, you only have room for short gaps. Start spacing from the first lesson.
- Dropping a topic once it feels known. Feeling sure is exactly when the next review is cheapest.
Sources
- [1]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, 132(3), 354–380. doi.org/10.1037/0033-2909.132.3.354
- [2]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, 19(11), 1095–1102. doi.org/10.1111/j.1467-9280.2008.02209.x
- [3]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, 14(1), 4–58. doi.org/10.1177/1529100612453266
- [4]Roediger, H. L., & Karpicke, J. D. (2006). Test-enhanced learning: Taking memory tests improves long-term retention. Psychological Science, 17(3), 249–255. doi.org/10.1111/j.1467-9280.2006.01693.x