The Leitner system: how to review flashcards with boxes

The Leitner system sorts flashcards into several boxes that you review at different frequencies. If you answer a card correctly, it moves to the next box and you see it less often; if you miss it, it goes back to the first box and you see it soon. That way you spend more time on what is hard and less on what you already know.

The method is credited to Sebastian Leitner, a German science writer who popularized it in the 1970s. Its appeal is that it needs no software: a stack of cards, a few boxes or envelopes and a calendar are enough. The underlying idea is the same one spaced repetition apps use.

Kornell (2009) ran flashcard experiments with vocabulary and compared two ways to study the same material: one large stack, where each card came back after a long gap, and several small stacks, where cards repeated almost immediately. The large stack led to better recall for most participants, even though many believed the small stacks had worked better for them.

The meta-analysis by Cepeda and colleagues (2006) points the same way for verbal recall tasks: spreading practice out usually leads to better retention than cramming it together. The Leitner system is a manual way to apply that principle. None of these studies tested Leitner boxes specifically, so the exact schedule is a practical choice, not a proven number.

You need five numbered boxes or envelopes, index cards and a pencil. Write one question per card with the answer on the back. Every new card starts in box 1. This schedule is a common example that you can adjust to your deadline:

The core rule is simple: answer before you look at the back. If your answer was complete, the card moves up one box. If you missed it or only recognized it once you saw it, it returns to box 1, even if it was in box 4. The penalty feels harsh, but it stops a weak card from disappearing for weeks.

Decide in advance what counts as correct. For vocabulary, it might mean spelling the word without mistakes; for a concept, explaining both ideas the answer asks for. If you allow half-right answers, the higher boxes fill up with cards you do not really know, and the system stops doing its job.

On Monday you create ten German cards and review them: you get six right, which move to box 2, and miss four, which stay in box 1. On Tuesday you review only box 1; you get three of those four right and they move to box 2. On Wednesday both box 1 and box 2 are due, and box 2 now holds nine cards.

If on Wednesday you miss a box 2 card, say “der Schlüssel” (the key), it goes back to box 1. After two weeks, the easy words sit in boxes 4 and 5 while the hard ones keep showing up daily. Add new cards in small batches so box 1 never overflows.

Most problems come from adding too much or skipping days. If you miss a week, do not try to catch up on every box at once: start with boxes 1 and 2, which are the most urgent, and work through the others over the next few days.

Spaced repetition apps apply the same logic without physical boxes: they record how you answered and work out when to show each card. The difference is that instead of five fixed levels, they usually use intervals that grow more gradually and adjust card by card.

Your part does not change: writing good questions, answering before you look and rating yourself honestly. If you prefer paper, the Leitner system is still a sound option, especially for a small syllabus or when you want to study away from screens.

Lumia AI does not use Leitner boxes, but it applies the same idea through ratings. After answering, you choose Again, Hard, Good or Easy, and Lumia calculates the next review date: cards you miss come back soon, and cards you know get spaced further apart.

You can create cards by hand, organize them in books and add an optional hint. If you generate a draft with AI from your notes or a PDF, check every question before studying it. The rating is your judgment: Lumia does not automatically grade whether an open answer was complete.