Spaced repetition and active recall: a study guide for students

§ 1The forgetting curve

In the 1880s Hermann Ebbinghaus learned lists of nonsense syllables and measured how much faster he could relearn them after different delays, published in 1885 as Über das Gedächtnis. Forgetting was fast at first and slowed down later. Murre and Dros repeated the experiment in 2015 and obtained a very similar curve. The lesson for students is not that forgetting is bad, but that a review is best timed for when the memory has started to fade.

§ 2Active recall: testing is studying

Roediger and Karpicke (2006) gave students short texts to learn. Some read a text four times; others read it once and practised recalling it three times. On a test five minutes later, rereading came out slightly ahead. A week later the result reversed: the recall group remembered 61% and the rereading group 40%. The rereaders also felt more confident, which is why rereading is so tempting.

Karpicke and Roediger (2008) found that once a word had been recalled correctly, studying it again added nothing to later recall, while testing it again helped a lot. Producing an answer also beats recognizing one: a meta-analysis by Rowland (2014) found larger benefits from tests where you recall the answer than from tests where you pick it from options.

§ 3Spacing: why cramming fails

Cepeda and colleagues (2006) pooled 839 comparisons from 317 experiments. With the same total study time, spaced practice led to 47% recall and massed practice to 37%. A later study with more than 1,350 participants (Cepeda and colleagues, 2008) showed that the best gap between sessions grows with how long you need to remember: for a test a week away, the best gap tested was one day; for a test about a year away, it was three weeks.

Spacing also feels worse than it is. In Kornell’s 2009 flashcard study, spacing was more effective for 90% of participants, yet after the first session 72% believed cramming had worked better. Expect spaced study to feel harder, and do not let that feeling decide for you.

§ 4A weekly plan that uses both

1. After each class or chapter, write short notes in your own words and turn the key facts into questions.
2. The same day, close the notes and answer the questions from memory. Check, and mark what you missed.
3. The next day, answer them again, only from memory.
4. Then let the gaps grow: a few days, a week, two weeks. Questions you miss come back sooner.
5. Mix some older material into every session, so each review covers a little of everything.
6. Before the exam, do practice tests under exam conditions instead of rereading.

A spaced-repetition app does the scheduling for you. Modern schedulers such as FSRS (Free Spaced Repetition Scheduler) estimate, card by card, how likely you are to remember, and bring a card back when that chance falls to the level you choose.

§ 5Writing good cards

• One fact per card. A card that asks for a list of five things is five chances to fail; split it, or put the list in a memory palace.
• Ask for the answer in your own words, not a copied sentence.
• Add a word of context when two cards look alike.
• Make cards from notes you understand. Memorizing something you have not understood is slow and brittle.
• Rewrite or delete cards you keep failing; they are usually badly worded rather than too hard.

§ 6What else helps, and what helps less

In a large review of study techniques, Dunlosky and colleagues (2013) rated practice testing and distributed practice as the two techniques of high utility, and rereading and highlighting as low. Interleaving, mixing different kinds of problems, helps when you need to tell similar types apart, such as kinds of maths problems, but a meta-analysis by Brunmair and Richter (2019) found that it can hurt when learning lists of words. Sleep makes a real but modest contribution to consolidation (Cordi and Rasch, 2021), and a night without sleep clearly impairs learning new material the next day (Yoo and colleagues, 2007).

Questions and answers

What is the difference between active recall and spaced repetition?

Active recall is how you review: by bringing the answer back from memory. Spaced repetition is when you review: at growing intervals. They work best together.

How many new flashcards should I add per day?

Few enough that your daily reviews stay manageable. Every new card brings future reviews with it, so a modest number kept up for weeks beats a large batch you abandon. Mindhall’s default is 15 new cards a day.

Is cramming ever useful?

Cramming can help on a test the next morning, but crammed material is forgotten quickly. If you need it after the exam, space it.

What is FSRS?

FSRS (Free Spaced Repetition Scheduler) is an open-source scheduling algorithm. It models how stable and how difficult each memory is and schedules the next review for when your chance of recall falls to a target you set.