Retrieval Practice and Spacing: Learning That Lasts

Most of us were taught to revise by rereading notes and highlighting the important bits. It feels productive: the material looks familiar, and familiarity feels like knowing. A large body of research in cognitive psychology suggests this feeling is misleading, and that some less comfortable methods produce far better long-term memory.

Bringing it back out: the testing effect

Retrieval practice means recalling information from memory, rather than reviewing it. Answering quiz questions, writing down everything you remember about a topic, or explaining an idea to someone without notes are all retrieval.

A widely cited demonstration comes from Henry Roediger and Jeffrey Karpicke (2006), published in Psychological Science. University students read short prose passages. Some then restudied the passage; others took a free-recall test, writing down as much as they could remember, with no feedback. A final test came after five minutes, two days or one week.

At five minutes, the students who had restudied did better. At two days and one week, the pattern reversed: those who had been tested remembered substantially more. The students who had restudied also felt more confident that they would remember. Their predictions were wrong.

This is the testing effect. Pulling information out of memory seems to change the memory itself, making it easier to retrieve again later. Testing is usually thought of as a way of measuring learning. Roediger and Karpicke’s results suggest it is also a way of producing it.

Does it work in real classrooms?

Laboratory results do not always survive the move to schools. Pooja Agarwal, Ludmila Nunes and Janell Blunt (2021) systematically reviewed 50 experiments carried out in real classrooms, from primary schools to medical schools. A majority (57%) of the effects were medium or large, and benefits appeared across subjects, ages and types of test. One caution: almost all of the studies came from the United States and Western Europe.

Spreading it out: the spacing effect

The idea that timing matters goes back to Hermann Ebbinghaus, a German psychologist who in the 1880s tested his own memory for lists of nonsense syllables. His results, published in 1885, produced the first “forgetting curve”: memory falls away quickly at first, then more slowly. He also noted that repetitions spread over several days were more efficient than the same number crammed into one sitting.

More than a century later, Nicholas Cepeda, Harold Pashler, Edward Vul, John Wixted and Doug Rohrer (2006) combined 317 experiments on spacing in a review in Psychological Bulletin. They confirmed that spacing study sessions apart produced better retention than massing them together. They also found that the best gap between sessions depends on how long you need to remember: the further away the test, the longer the ideal gap.

For a spelling test on Friday, a few short practices across the week will do better than one long session on Thursday night. For a GCSE exam next summer, topics need to be revisited over weeks and months.

Mixing it up: interleaving

Most textbooks and worksheets practise one type of problem at a time: twenty questions on area of a triangle, then twenty on area of a circle. This is blocked practice. Interleaving mixes different types together.

Doug Rohrer and Kelli Taylor (2007) taught university students to calculate the volumes of four unfamiliar solids, such as a wedge and a half cone. During practice, the students who worked in blocks scored higher (89% against 60%). On a test a week later, the result flipped: students who had practised the problem types mixed together scored 63%, while the blocked group scored 20%.

A likely reason is that blocked practice tells you which method to use before you start. Interleaving forces you to work out which method fits the problem, which is what a real test demands. The evidence for interleaving is strongest in maths and in learning to tell categories apart; it is less established in other subjects.

Why these methods feel worse

The psychologist Robert Bjork (1994) described conditions like these as “desirable difficulties”: they make learning feel slower and more effortful, yet produce stronger memory. That mismatch matters. In the Roediger and Karpicke study, students preferred the method that worked less well. Children, and adults, need to know that struggling to remember something is a normal part of learning, not a sign of failure.

A large review by John Dunlosky and colleagues (2013) rated ten common study techniques. Practice testing and distributed practice were the only two rated as having high utility. Rereading and highlighting were rated low.

In the classroom

• Start lessons with a short, low-stakes quiz on material from last week, last month and last term. Keep it unmarked or self-marked so it feels like practice.
• Use “brain dumps”: two minutes to write everything pupils remember about a topic, then compare with notes to fill gaps.
• Give feedback. Retrieval with corrective feedback helps pupils fix errors instead of strengthening them.
• Plan for revisiting. Build earlier topics into homework and starter tasks instead of leaving them until exam season.
• Mix problem types in practice once pupils can do each type on its own.
• For pupils with SEND, keep quizzes short, offer multiple-choice or picture options where needed, and remove time pressure. The aim is practice in recalling, not a test of speed.

At home

You do not need to be an expert in the subject to help with retrieval.

• Ask your child to teach you what they learned today, without looking at their book.
• Turn spellings, times tables or key vocabulary into quick quizzes in the car or over dinner.
• Make flashcards together, with a question on one side and the answer on the other. Encourage your child to say the answer aloud before turning the card.
• Spread practice out: ten minutes on three evenings beats thirty minutes the night before.
• Keep it light. The aim is a bit of effort, not anxiety. If quizzing causes distress, ease off and talk to the teacher.

Further reading

• Agarwal, P. K., Nunes, L. D. and Blunt, J. R. (2021). Retrieval practice consistently benefits student learning: a systematic review of applied research in schools and classrooms. Educational Psychology Review.
• Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T. and Rohrer, D. (2006). Distributed practice in verbal recall tasks: a review and quantitative synthesis. Psychological Bulletin, 132(3), 354-380.
• Dunlosky, J., Rawson, K. A., Marsh, E. J., Nathan, M. J. and Willingham, D. T. (2013). Improving students’ learning with effective learning techniques: promising directions from cognitive and educational psychology. Psychological Science in the Public Interest, 14(1), 4-58.
• Bjork, R. A. (1994). Memory and metamemory considerations in the training of human beings. In J. Metcalfe and A. Shimamura (eds), Metacognition: Knowing about Knowing (pp. 185-205). MIT Press.
• Ebbinghaus, H. (1885/1913). Memory: A Contribution to Experimental Psychology (trans. H. A. Ruger and C. E. Bussenius). Teachers College, Columbia University.
• Roediger, H. L. and Karpicke, J. D. (2006). Test-enhanced learning: taking memory tests improves long-term retention. Psychological Science, 17(3), 249-255.
• Rohrer, D. and Taylor, K. (2007). The shuffling of mathematics problems improves learning. Instructional Science, 35(6), 481-498.