Active recall: the most effective review technique

What is active recall?

Active recall, also called retrieval practice or the testing effect, means going to fetch information from your memory rather than re-reading it. Instead of going over your chapter on photosynthesis one more time, you close the book, write down everything you remember, then compare.

The principle is simple, the effect is massive, and yet it's rarely practiced. Most people review by re-reading and highlighting, two of the least effective techniques according to Dunlosky and colleagues' landmark 2013 review.

The experiment that changed everything

In 2006, Henry Roediger and Jeffrey Karpicke, at Washington University in St. Louis, had students study a scientific text. One group read it four times in a row. Another read it once, then tried three times to rewrite it from memory.

Five minutes later, the re-readers did better: 81% versus 75%. A week later, everything flipped: 61% for those who tested themselves, 40% for those who re-read. Over the course of the study, the re-readers had nonetheless read the text 14 times on average, versus 3.4 times for the others.

Another telling detail: it was the re-readers who believed they were best prepared. Re-reading creates a feeling of mastery; testing builds it.

Why testing yourself leads to better retention

Every time you retrieve information from memory, you strengthen the path that leads to it. Re-reading is looking at that path on a map. Recalling is walking it on foot.

This last point is surprising: in 2011, Jeffrey Karpicke and Janell Blunt showed in the journal Science that practicing retrieving a text led to better learning than building concept maps, a technique otherwise well regarded for organizing knowledge. Robert Bjork calls these "desirable difficulties": what makes learning a bit harder in the moment makes it more durable.

6 ways to practice active recall

1. 01The blank pageAfter a lesson, write down everything you remember on a blank sheet. Then compare with the course and fill in with a different color.
2. 02Questions before answersTurn your notes into questions: "Why…?", "What's the difference between…?", "What happens if…?".
3. 03Question-answer flashcardsA question on the front, a short answer on the back. Answer out loud before flipping the card.
4. 04QuizzesMultiple-choice questions with plausible wrong answers and an explained correction.
5. 05Explaining out loudExplain the concept as if to a beginner friend. Wherever you hesitate, you've found what needs review.
6. 06Redoing without lookingFor skills, math, code or languages, active recall means redoing the exercise without the solution in sight.

Pitfalls to avoid

• Looking at the answer too fast. Give yourself time to search, even thirty seconds. It's the effort that counts.
• Not correcting yourself. Testing yourself without checking can cement a mistake. Immediate correction strengthens the testing effect, even for multiple-choice.
• Questions that are too easy. If you get everything right, raise the difficulty: open questions, case studies, new exercises.
• Doing it all at once. Space out your recall sessions: it's the combination of the two that gives the best results.

Active recall and multiple-choice: what's a quiz worth?

Multiple-choice questions are convenient, but less demanding than an open question: recognizing the right answer is easier than retrieving it. They remain useful, especially with plausible options and a correction that explains why. The ideal: alternate multiple-choice, open questions, and exercises where you have to produce something.

A typical 25-minute session

1. 0-10 minLearnOne concept, with an example.
2. 10-15 minBlank pageEverything you remember, without looking.
3. 15-20 minCorrectCompare, fill in, note what was missing.
4. 20-25 minGo backThree questions on the previous session, from memory.