Spaced repetition is one of the few study techniques with genuinely strong, long-standing research support behind it — not a marketing term, but a specific, well-studied approach to scheduling review.
In the 1880s, psychologist Hermann Ebbinghaus ran a series of memory experiments on himself and plotted how quickly newly learned material fades without review — a steep initial drop, then a slower decline. This "forgetting curve" showed that most forgetting happens soon after learning, not gradually over months, which is exactly why reviewing something once and assuming it's "learned" fails so often.
A separate, robust finding — the spacing effect — shows that review sessions spread out over time produce stronger, longer-lasting memory than the same number of reviews crammed close together. Cramming can feel more effective because it boosts short-term recall, but spaced review consistently wins for what you can still recall days or weeks later.
A spaced-repetition system tracks each item you've learned and estimates when you're likely to start forgetting it, based on your past performance on that specific item. Items you consistently get right are pushed further apart; items you get wrong come back sooner. The review schedule is personalized to what you actually know, not a fixed calendar applied to everyone.
A fixed weekly review of everything you've ever learned wastes time re-reviewing material you already know solidly, while under-reviewing material you're shakier on. A spaced system concentrates review time where it's actually needed, which is why it consistently outperforms flat, non-adaptive review schedules for the same amount of study time.
See also the reference page: Learn Languages with Tarc.
A pattern first documented by psychologist Hermann Ebbinghaus in the 1880s, showing that newly learned material is forgotten quickly at first, then more slowly over time — most of the loss happens soon after learning, not gradually over months.
A well-documented finding that review sessions spread out over time produce stronger long-term memory than the same number of reviews crammed close together, even though cramming can feel more effective in the short term.
It tracks your past performance on each specific item and estimates when you're likely to start forgetting it — items you consistently get right are spaced further apart, while items you get wrong come back sooner.
For most learners, yes — a fixed schedule wastes time re-reviewing material you already know well while under-reviewing material you're weaker on, while spaced repetition concentrates review time where it's actually needed.