What Is the Leitner System? Spaced Repetition That Brings Back the Words You Miss

In 1972, Sebastian Leitner published a book in Germany called So lernt man lernen (“How to learn to learn”). In it he described a way of managing flashcards in a box with dividers. Cards you know move towards the back; cards you get wrong go back to the front. The front cards are reviewed often, the back ones only occasionally. Today this is called the Leitner system, and it sits behind the review schedule of many vocabulary apps.

This post covers why the Leitner system works, how to run it with paper cards, and how it compares with other methods.

Spaced reviews last longer

The Leitner system rests on two effects that psychologists have known about for a long time.

The first is the spacing effect. For the same number of reviews, spreading them out over days helps you remember for longer than repeating them all at once. Memory research goes back to 1885, when Hermann Ebbinghaus tested himself on lists of nonsense syllables. A great deal of work has followed. In 2006, Cepeda and colleagues published a meta-analysis in Psychological Bulletin that pulled together many experiments on verbal learning and confirmed that spaced practice beats massed practice.

The second is the testing effect. Trying to recall an answer with it covered leaves a stronger memory than looking at it and reading it again. In a 2008 study in Science, Karpicke and Roediger had students learn Swahili-English word pairs. Students who kept being tested remembered them well a week later. Students who, once they had recalled a word correctly, only went on studying it without further tests forgot far more.

Covering the answer on a flashcard uses the testing effect. Reviewing each section of the box at a different interval uses the spacing effect. The Leitner system is a way of putting both into practice with nothing more than a paper box.

Why missed words come back sooner

The heart of the Leitner system is that not every word gets the same number of reviews.

Reviewing words you already know every day doesn’t gain you much. Seeing a word you recall easily, again and again, just uses up time. A word you get wrong, on the other hand, is a sign that you haven’t learned it yet. Words like that need another chance to be recalled before they are forgotten completely.

So words you get right move to a section further back, and the gap before the next review grows. Words you miss go back to the front, so you meet them again soon. Most of your review time ends up going to the words you don’t know yet. In the Leitner system as it is usually described, a card you miss goes back to the first section, wherever it was.

Doing it with paper cards

You don’t need an app. Cards about the size of a business card and a box with five sections are enough.

1. Write the English word on the front and the meaning on the back. Adding the sentence where you met the word gives you a clue for recalling it.
2. Every new card starts in section 1.
3. Look at the front, recall the meaning, then turn the card over to check. Cards you recalled move to the next section; cards you didn’t go back to section 1.
4. When you get a card right in section 5, take it out of the box.

There are several ways to decide when to review each section. One is by the calendar: for example, section 1 every day, section 2 every two days, section 3 once a week, section 4 every two weeks and section 5 once a month. The exact numbers don’t matter much. What matters is that the further back a section is, the longer the gap.

Paper cards have two strengths: writing them out helps you remember, and one look at the box shows how many words are at each stage. Their weaknesses are the time it takes to make cards and having to remember yourself which section is due.

How to build a word list from your reading is in Build Your English Vocabulary Notebook from Your Own Reading. Turning the words in that notebook into cards for this box works well too.

How it differs from Anki

Among spaced repetition apps, Anki is the best known. In Anki, after you see the answer you rate yourself, with buttons such as Again, Hard, Good and Easy, and the next interval is calculated for each card from your rating. Instead of fixed stages like the sections of a Leitner box, each card’s interval is adjusted finely.

Which is better depends on the person. If you want to rate yourself and fine-tune, something like Anki suits you. If deciding on a rating feels like a chore, or you like to see your progress as stages, the simplicity of the Leitner system suits you. Because it is simple, it is also easy to understand why a particular word came up today.

What every method has in common is that the spacing only works if you open it on the days reviews are due. Ten cards every day fits the idea of the Leitner system better than a hundred once a week.

How ABC George reviews words

ABC George, an app I make for iPhone and iPad, lets you read Project Gutenberg classics with a built-in dictionary. It is free, with no ads and no in-app purchases, and the dictionary works without a connection.

Long-press a word in the text and tap Look up, and the word is saved to the Word Book in the Words tab, together with its meaning and the sentence you met it in. That word book works as a Leitner box.

A newly saved word is due for review straight away. In the Quiz tab, choose “Due for review” and only today’s words come up. Get a word right and it moves up a step, and the gap before you see it again grows. With each correct answer the gap stretches, to the next day, then a few days, then a week, and at the top step it is about five weeks. Get it wrong and it drops one step and is due again straight away. The difference from the usual Leitner system above is that a miss drops a word only one step rather than all the way back to the start. A word you knew well doesn’t go back to square one because of a single mistake.

Under each word in the word book are five small bars, which fill in one by one as the word climbs. It is the same as seeing which section of a paper box a card is in. When all five are filled, the word is Mastered, and you can view mastered words separately with the word book’s filter. The Quiz screen shows your saved words, how many are due now, how many are mastered, and your accuracy.

You don’t rate yourself; the quiz checks your answer. You can choose from four question types: Fill in the blank, which puts the word back into the real sentence where you met it; Word → meaning, where you choose the definition; Meaning → word, where you choose the word; and Spelling, where you type it. All of them ask you to recall with the answer hidden, in line with the testing effect.

You can set a daily quiz target with “Daily goal” in Settings; it starts at 20. Keeping up daily is in Practical Tips for Reading with ABC George Every Day, vocabulary size is in How Many English Words Do You Need to Read a Novel?, and Getting Started with ABC George walks through your first book.