Spreading learning out beats cramming

In one line: spreading study out with gaps helps people remember more than doing it all at once, and the longer you need to remember something, the longer the gaps should be.

What they did

This isn’t a new experiment. It’s a review: Nicholas Cepeda and four colleagues in the USA gathered up the existing research on spacing and combined the results.

They found 184 published articles, going back more than a century. Between them, these held 317 experiments and 839 comparisons of spaced and bunched-up study. All of them tested memory for words or facts, such as word lists or vocabulary.

They asked two questions. Does spacing help? And how long should the gap be, if you want to remember something for a day, a week or a year?

What they found

• Spacing helps. On average, people recalled about 47% after spaced study, against about 37% after studying in one go, for the same total study time. The gap tended to be larger when the test came after a longer delay.
• It held up widely. The benefit held across the wide range of verbal-learning studies and delays the review covered.
• The best gap depends on how long you need to remember. The further away the test, the longer the best gap between study sessions.
• Gradually longer gaps aren’t clearly better. Making each gap longer than the last is a popular approach, used by flashcard apps. The evidence that it beats evenly spaced gaps is mixed.

How much should you trust it?

Strong evidence that spacing helps memory for facts; the best gap is a rough guide.

• This pulls together hundreds of experiments, so the main finding is very solid.
• All of the studies used words and facts. They don’t tell us directly about hands-on skills, clinical reasoning or changing what people do at work.
• Most were in labs or classrooms, with students. Busy wards and clinics bring interruptions and tiredness that the studies didn’t include.
• The advice on gap length comes mainly from a later study by the same team (see the small print), so treat it as a rough guide, not an exact rule.

If you need to convince someone

In our words (a paraphrase of Cepeda et al., 2006 and 2008, not a quotation): the longer you need people to remember something, the longer the gaps between reminders should be. For something people need all year, think weeks between reminders, not days.

What it means for you

1. Decide how long it needs to last. Start with what people need to do differently, and for how long. A new process for next week needs a different plan from a skill for the whole year.
2. Match the gap to that. As a rough guide, for something needed in a week, come back after a day or two. For something needed all year, come back every few weeks.
3. Think again about once-a-year training. If content needs to last a year, the spacing research suggests that short, regular reminders (say monthly, such as a five-minute quiz at a team meeting) are likely to keep more of it alive than a single annual session. This is an extrapolation from lab studies, not something that has been tested directly.
4. Tell people why. “I’m asking you this because you’ll have started to forget it since we last met. Pulling it back out now helps it last.”

How it appears in Teaching That Lands

The sessions are a week apart. By the rough guide, a week’s gap suits remembering something for about a month, which fits a three-week course. For a year, the spacing needs to carry on after Session 3.

The retrieval happens in the room: each session opens by recalling the last one, a week later. Session 2 opens with people showing what they did with their Session 1 ask, then a quick quiz on Session 1. Session 3 opens with a surprise retest from Session 2, then participants run their own quizzes on the group. Between sessions, the message people get only reminds them of the ask they wrote down. In Session 3, participants plan what their own learners will revisit at 30, 60 and 90 days.

The small print

• “Massed” practice means all at once; “distributed” or “spaced” practice means spread out with gaps. The gap between sessions is the “lag”; the time until the test is the “retention interval”.
• The rule of thumb comes from a follow-up experiment with more than 1,350 learners (Cepeda et al., 2008, Psychological Science). The best gap was about 20–40% of the delay when the test was a week away, falling to about 5–10% when it was a year away. So for a year, a gap of roughly three to five weeks.
• On gradually longer gaps, the review found only a small, tentative advantage from few studies. A later study (Karpicke & Roediger, 2007) found equal gaps as good or better for long-term memory.
• Spacing is different from interleaving, which mixes kinds of problem together and has its own research.
• The first person to measure spacing was Ebbinghaus, in 1885.