You learn something on Monday. By Friday, most of it has gone. This is not a personal failing; it is how memory works. The good news is that forgetting follows a pattern, and you can plan around it.
The forgetting curve
In the 1880s, the German psychologist Hermann Ebbinghaus spent years memorizing lists of nonsense syllables and testing himself at different intervals. He found that he lost most of a new list within the first day or two, after which the forgetting slowed down. Plotted on a graph, it makes the now-famous forgetting curve: a steep drop followed by a long, flat tail.
He also found something more useful. Each time he relearned a list, it took less effort than the time before, and the next round of forgetting was slower. Reviewing does not just top up a memory. It changes how long the memory lasts.
Why spacing beats cramming
Cramming can get you through tomorrow's quiz. It does very little for next month's exam. Research on the spacing effect, going back more than a century, consistently finds that the same amount of study time produces much more durable learning when it is spread over days or weeks rather than packed into one session.
Part of the reason is that a review works best when the memory has started to fade but has not disappeared. Reviewing ten minutes after learning is too easy: nothing has been forgotten, so there is little to strengthen. Reviewing after three weeks may be too late. The sweet spot is in between, and it moves further out each time you successfully remember.
A simple schedule
You do not need software to start. This expanding schedule works for most school and college material:
| Review | When | What to do |
|---|---|---|
| 1 | Same day or next day | Short quiz or a blank-page recall of the new material |
| 2 | About 3 days later | Quiz again and mark what you missed |
| 3 | About a week later | Mixed questions from the whole topic |
| 4 | 2 to 3 weeks later | Practice test under exam conditions |
| 5 | Before the exam | Only the items that are still shaky |
If you get something wrong, shorten the gap for that item and bring it back sooner. If it was easy, stretch the gap. That is the whole idea behind every spaced repetition system.
Two classic systems
The Leitner box
In the 1970s, the German science writer Sebastian Leitner described a method that uses a box of flashcards divided into sections. New cards go in section 1, which you review often. When you answer a card correctly, it moves up a section, which you review less often. When you get it wrong, it goes back to section 1. You can build one with a shoebox and index cards, or with five envelopes.
Algorithms: SM-2 and its descendants
In 1987, Piotr Woźniak created the SM-2 algorithm for his SuperMemo software. After each review you rate how well you remembered an item, and the algorithm calculates when you should see it next. Many flashcard apps have used SM-2 or variations of it for years. The math matters less than the principle: easy items fade into the background, and hard ones keep coming back.
How far apart should reviews be?
It depends on how long you need to remember. Studies by Nicholas Cepeda and colleagues suggest that the best gap between study sessions grows with the time until the test: a few days apart for an exam in a couple of weeks, and longer gaps for material you need for months. If your exam is close, keep the gaps short, but still leave at least a day between sessions.
Spaced repetition for teachers
- Spiral your quizzes. Include a couple of questions from two and four weeks ago in every quiz.
- Use warm-ups. The first five minutes of class are a good moment to retrieve older material.
- Teach students the schedule. Many students have never been told that spreading out study works better. Showing them the forgetting curve is often enough to change their habits.
Letting software do the scheduling
Keeping track of which topics are due is the tedious part. Quizbot's Exam Prep does it for you: you add your material and your exam date, take a short diagnostic quiz, and Quizbot builds a study plan by concept, with a next review date for each one. Practice sessions then reschedule each concept based on how you did, and a daily review reminder tells you what is due. You can also turn any chapter into a quiz with the AI quiz generator and put it on your own schedule.
Key points
- Forgetting is fast at first and then slows down. Each review resets the curve and makes it flatter.
- Spread the same study time over several sessions instead of one long one.
- Test yourself during each review rather than rereading.
- Bring back what you miss sooner, and what you know later.
