The Leitner system: how the flashcard box method works

What is the Leitner system?

The system is named after Sebastian Leitner, a German science journalist who described it in his 1972 book So lernt man lernen ("How to learn to learn"). His idea was a card box with several compartments. Instead of going through a whole deck every time, you sort cards by how well you know them, and you spend most of your time on the ones you don't.

The appeal is that the box makes the decisions for you. You never have to ask "should I review this card today?" The box it is sitting in answers that. You can run it with a shoebox and index cards, with envelopes, or with folders in a flashcard app that lets you sort cards into groups.

How to set up the Leitner system, step by step

The version most students use today has five boxes and a review schedule in days. The exact gaps below are one sensible choice, not a rule from the book.

1. Make your boxes. Label five boxes, envelopes or app folders 1 to 5.
2. Give each box a review gap. For example: box 1 every day, box 2 every 2 days, box 3 every 4 days, box 4 once a week, box 5 every two weeks. Write the schedule on the lid.
3. Put every new card in box 1. Add new cards in small, steady batches. Our guide to how many flashcards a day explains why the number of new cards drives your whole workload.
4. On each study day, review only the boxes that are due. Box 1 every time, then whichever others the schedule says.
5. Say or write the answer before you turn the card over. Recognising the back of the card is not the same as producing it. If you only "kind of" knew it, count it as wrong.
6. Move each card. Right: up one box. Wrong: back to box 1 (more on this below).
7. Keep box 5 in play. Cards that reach the last box stay there and keep being reviewed on its schedule until your exam.

If you start studying from a deck that is already written, put everything in box 1 on day one and let the first few sessions sort it. Cards you know well will climb out quickly.

What do you do with a card you get wrong?

In the classic rule, a missed card goes all the way back to box 1, wherever it was. That sounds harsh for a card that failed once in box 4, but it is the point: if you could not recall it after a long gap, the gap was too long for that card, and it needs to be rebuilt with frequent practice.

Some people use a gentler version, where a missed card drops down just one box. That is reasonable for big decks where box 1 would otherwise overflow, or for cards where you got most of the answer. A simple compromise:

• Completely blank: back to box 1.
• Partly right, or right after a long struggle: down one box.
• Missed three or more times in a row: the card is the problem, not your memory. Split it into smaller cards or rewrite it. Our guide on how to make good flashcards covers the usual fixes.

Before you put a missed card back, look at the correct answer properly, and check it against your notes or textbook. A card you get wrong and never correct just teaches you the wrong thing again.

Why does the Leitner system work?

The box does nothing magic. It enforces two study habits with some of the strongest evidence behind them.

It makes you retrieve. Every review is a small test: you try to recall the answer before you see it. Dunlosky and colleagues (2013) reviewed ten common study techniques and gave practice testing a high utility rating, while rereading and highlighting were rated low. Karpicke and Roediger (2008) also found that continuing to test items after students had recalled them correctly produced a large boost in later recall, while repeated studying of those items had no effect. Moving cards up a box instead of out of the box keeps that testing going.

It spaces the cards you know. Each step up lengthens the gap before you see a card again. A meta-analysis by Cepeda and colleagues (2006) pulled together 839 assessments of distributed practice from 317 experiments, across 184 articles. One of its main conclusions is that the best gap between sessions got longer as the time you need to remember for got longer. Kornell (2009) tested spacing with flashcards themselves: studying one large stack, which spaced out each card's repetitions, beat several small stacks studied separately for 90% of participants. Yet after the first session, 72% believed the small stacks had worked better.

That last finding is why a fixed system helps. Spacing feels worse while you are doing it, so left to our own judgement we tend to mass practice. The box removes the choice. For more on choosing gaps, see our spaced repetition schedule.

What are the limits of the Leitner system?

• Fixed gaps ignore your exam date. The ideal gap depends on how long you need to remember something, as Cepeda and colleagues (2006) found. If your exam is in ten days, a two-week box 5 never comes round. Shrink the gaps when the exam is close and stretch them when it is months away.
• It trusts your marking. The whole system depends on an honest right or wrong. Kornell and Bjork (2008) studied students who were allowed to drop flashcards they thought they knew, and found that being allowed to drop cards had small but consistently negative effects on learning. The authors trace the problem partly to students' shaky judgements of which cards they already knew. Strict marking, and never retiring cards before the exam, protects you from the same mistake.
• Box 1 can pile up. Add too many new cards at once and box 1 becomes a daily wall. Slow the new cards down until it clears.
• Cards suit facts better than reasoning. Definitions, vocabulary, drug names and dates fit on a card. Explaining a process, applying a formula or answering a long question needs practice questions and past papers too.
• Someone has to write the cards. Making good cards takes real time, and that time is not practice.

If writing cards is the part that stops you, Ace turns material you already have, such as a PDF, PowerPoint slides or Word documents, into practice questions written only from that material, and you pick which chapters to study. Each answer shows the sentence from your file that backs it, so you can check a miss straight away. Streaks and a study calendar help you keep showing up on the days your reviews are due. The how it works page shows the steps.

Frequently asked questions

Sources

1. Leitner, S. (1972). So lernt man lernen: Angewandte Lernpsychologie, ein Weg zum Erfolg. Freiburg im Breisgau: Herder. (Deutsche Nationalbibliothek record.)
2. 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.
3. Kornell, N. (2009). Optimising learning using flashcards: Spacing is more effective than cramming. Applied Cognitive Psychology, 23(9), 1297–1317.
4. Kornell, N., & Bjork, R. A. (2008). Optimising self-regulated study: The benefits and costs of dropping flashcards. Memory, 16(2), 125–136.
5. Karpicke, J. D., & Roediger, H. L. (2008). The critical importance of retrieval for learning. Science, 319(5865), 966–968.
6. 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.