The forgetting curve: what Ebbinghaus actually found, and what to do about it

Evidence grade: STRONG. The steep-then-flattening shape of forgetting is among psychology's oldest replicated findings — including a faithful modern replication of the original method. The classroom-relevant refinements (what slows the curve, what forgetting is for) are equally solid.

In the 1880s Hermann Ebbinghaus memorized thousands of nonsense syllables and tested himself at intervals — the first quantitative study of memory, run on a sample of one. His curve became famous: forgetting is fastest immediately after learning, then decelerates — a steep early plunge flattening into a long tail. The finding has survived everything since, including a 2015 direct replication of the original protocol (Murre & Dros), which is more than most century-old psychology can say.

Reading the curve correctly

Three refinements separate productive use from poster-grade fatalism:

1. The curve describes unreinforced memory for meaningless material. Ebbinghaus used nonsense syllables deliberately — meaning was the variable he was controlling away. Meaningful, structured, connected material forgets far more slowly; the dramatic "students forget 70% within a day!" numbers quoted from the curve describe cram-learned arbitrary content, not well-taught concepts. (Those percentage claims are also usually quoted without the retention interval or material type — treat any specific figure with suspicion; the shape is the finding.)

2. Each retrieval resets the curve — shallower. This is the load-bearing fact: successful retrieval at the right moment doesn't just restore the memory, it flattens its subsequent forgetting — each well-timed re-encounter yields a slower-decaying curve than the last. Stack these and you get the spacing schedule: review intervals that grow as the curve flattens, which is exactly what SRS systems automate.

3. "Forgotten" rarely means gone — the savings finding. Ebbinghaus measured relearning speed and found material he could no longer recall was relearned dramatically faster than new material. The practical meanings: apparent total forgetting usually isn't (the second teaching of anything is cheaper than the first — a reason to preview and revisit rather than teach-once-perfectly), and recall failure understates what remains. Bjork's new-theory-of-disuse framing sharpens this: retrieval strength (accessible now?) and storage strength (how well learned?) are different quantities — and the productive twist is that practicing at low retrieval strength builds more storage strength. Forgetting is the setup for the strengthening (desirable difficulties, at the memory level).

What the evidence doesn't say

It doesn't say a specific percentage is lost by a specific hour — the shape replicates; the poster numbers don't survive their missing context.
It doesn't make forgetting the enemy — unforgotten-because-just-reviewed material gains little from re-review; the curve's decline marks where practice pays.
It doesn't apply uniformly — meaningfulness, prior knowledge, and initial learning quality all bend the curve; the fatalist reading ("they'll forget it all anyway") ignores every lever teachers hold.

In the classroom

Schedule against the curve, not the calendar-unit: the return to a topic belongs days-then-weeks after teaching (the schedule), not solely at revision season.
Use the savings fact: brief revisits are cheap by design — "we're relearning, and relearning is fast" is both true and reassuring to children.
Interpret quiz failures with the two-strengths distinction: can't-recall-today is retrieval strength; it says less than it seems about what's stored — and the failed retrieval, followed by feedback, was itself productive.
Teach the curve to pupils — children who know forgetting is universal, expected, and the trigger for the practice that makes memory stronger stop reading it as personal failure. It's the cheapest metacognitive lesson available.

How Wiz Kids applies this

The review queue is a forgetting-curve tracker per skill per child: intervals lengthen as each skill's curve flattens (Leitner-style), a miss shortens them, and the fiction teaches the curve in child language — spells fade, and practicing one as it fades brings it back stronger. The savings principle shapes recovery too: a lapsed skill re-enters at short intervals, not back at the start, because relearning is fast and the system knows it.

References

Ebbinghaus, H. (1885). Über das Gedächtnis.
Murre, J. M. J., & Dros, J. (2015). Replication and analysis of Ebbinghaus' forgetting curve. PLOS ONE, 10(7).
Bjork, R. A., & Bjork, E. L. (1992). A new theory of disuse and an old theory of stimulus fluctuation. In From Learning Processes to Cognitive Processes.
Cepeda, N. J., et al. (2008). Spacing effects in learning: a temporal ridgeline. Psychological Science, 19(11) — the curve, weaponized into schedules.

© Glu IO Pty. Ltd. — Wiz Kids (wiz.kids). Link freely; republication requires permission — see terms. Found an error in our reading of the research? We correct fast: tell any teacher piloting Wiz Kids.