What Is the Leitner System? The Original Spaced Repetition

Short answer. The Leitner system is a flashcard organization method invented by German journalist Sebastian Leitner in 1972, using three to five physical boxes to schedule reviews at growing intervals. It's the original implementation of [spaced repetition](/blog/what-is-the-spacing-effect) and the conceptual ancestor of modern algorithms like [FSRS](/blog/what-is-fsrs).

How it works

You have several boxes (usually 5):

When you create a new card, it starts in Box 1. When you review a card:

Over time, the cards you find easy migrate to higher boxes (less frequent review); cards you struggle with stay in Box 1.

Why it works

The Leitner system implements two cognitive-science findings without needing any technology:

When to use Leitner today

Most students should use modern algorithmic spaced repetition tools (FSRS-based: Anki, SimpleQuizMaker review queue). But Leitner still has uses:

Leitner vs modern algorithms

Modern algorithms (FSRS, SM-2) improve on Leitner in two ways:

For most studiers, the modern algorithm is meaningfully better. But Leitner is still strictly better than no spaced repetition at all.

Setting up a physical Leitner system

The classic 5-box setup, with daily review schedule:

You need: 5 small boxes (shoebox, plastic dividers, drawer compartments), a stack of index cards (4×6 or 3×5), and a pen. Total setup time: 10 minutes. Daily review time: 15-25 minutes for a mature deck of 200-400 cards.

Failure cascading rules

The Leitner rule about failures is what gives it its spaced-repetition effect: when you get a card wrong, regardless of which box it lived in, it drops back to Box 1. This forces aggressive re-review of weak items. Strong items stretch out toward Box 5; weak ones stay in tight rotation.

Some Leitner variants soften this — drop one box on failure instead of all the way back — but the original Leitner cascade is closer to optimal for most learners. Software algorithms like FSRS make this more nuanced.

Why Leitner still gets taught

It's the most visually-obvious spaced-repetition method. The five physical boxes show the concept without any algorithm explanation needed. Teachers introducing spaced repetition to younger students often start with Leitner before moving them to algorithmic tools. Once the principle is internalised, software like Anki or SimpleQuizMaker's review queue does the same job with better tuning.

Related reading

The history: how Leitner systematized spaced practice

Sebastian Leitner, a German science journalist, formalized the system in his 1972 book *So lernt man lernen*. Before Leitner, students had been intuiting that "review the hard cards more often" worked, but no one had codified it into a procedure usable without electronics.

His insight: physical boxes with growing intervals would force spaced practice automatically, without any individual decision-making about when to review each card. The system became standard in language schools and self-study communities for decades before software replaced the boxes.

How the boxes work

A typical 5-box Leitner setup:

Mechanism:

The result: hard cards naturally get more practice; easy cards get less.

What Leitner's system got right

What it got wrong (vs. modern algorithms)

Modern alternatives

The mainstream replacements:

For most learners, FSRS-driven apps outperform Leitner by enough that the cleaner box version isn't worth the simplicity tradeoff.

When Leitner still wins

A few situations where the old system holds up:

For everything else, the digital algorithms are better.

Try modern algorithmic spaced repetition with a free quiz.