In the 1880s Hermann Ebbinghaus measured how quickly he forgot lists he had learned. The result, the forgetting curve, shows memory dropping fast at first and then more slowly. Every review resets the curve and makes it flatter.
Why spacing works
Reviewing right after learning is easy and does little. Reviewing just before you'd forget is harder, and that effort is what strengthens memory. Spaced repetition schedules each review for that moment.
The Leitner box system
In the 1970s Sebastian Leitner described a simple way to do this with flashcards in boxes. A card you answer correctly moves up a box and comes back less often; a card you miss goes back to the first box.
- Box 1: review today
- Box 2: in 1 day
- Box 3: in 3 days
- Box 4: in 7 days
- Box 5: in 14 days
- Box 6: in 30 days
Spaced repetition without the admin
The catch has always been making the cards. Type to Study makes them from your course automatically, one for each key term and one for each exam question, and follows a Leitner schedule for you. Missed cards come back in the same session and the next day; known ones after days, then weeks.