Interleaving: how to use mixed practice when you study

Interleaving is practising several kinds of problem or example in a mixed order, so that no two in a row need the same method. Its opposite, blocked practice, finishes one kind before starting the next, as most textbook exercises do. Interleaved practice feels harder and scores worse while you practise, then does better on a test days or weeks later, but only for some kinds of material.

This guide gives each study's sample, method, finding and limit, compares four universities' advice, and shows how to mix practice in maths, sciences, languages and essay subjects. Where the evidence is thin, as it is for essays, we say so.

EdCitation publishes this guide, and every study below was read in full in September 2026. We found them with EdCitation's Find sources, built the references in Cite a source and checked the list in Verify references. The session plan and the subject examples marked as ours are our own, and untested.

What is interleaving?

Interleaving is a way of ordering practice: problems A, B and C arrive as B, A, C, A, C, B rather than A, A, A, B, B, B, C, C, C. Rohrer et al. (2020) define an interleaved assignment as one in which no two consecutive problems need the same strategy, meaning a formula, a procedure or a concept.

Mixing does three things at once, those authors argue: you must choose the method from the problem itself, as in an exam; each kind of problem is spread out over time; and you must recall the method rather than copy it from the previous answer. Spacing and recall have guides of their own, on spaced repetition and retrieval practice.

What does the research on interleaved practice show?

The research shows a clear benefit for telling similar things apart, and none, or a cost, for some other material.

Rohrer and Taylor (2007): four solids

Rohrer and Taylor (2007) taught University of South Florida undergraduates the volumes of four unfamiliar solids, such as a wedge and a spheroid. Both groups did 16 practice problems in each of two sessions a week apart, seeing the solution after each. Blockers did four problems on one solid, then the next; mixers did the same problems shuffled. A week later all took a test of eight new problems.

In practice the blockers led, 89% against 60%. On the test, mixers scored 63% and blockers 20%, and almost every error was choosing the wrong formula. The limits, as the authors list them: 18 students finished, the setting was a laboratory, the test matched the practice, and the task was procedural.

Kornell and Bjork (2008): painters' styles

Kornell and Bjork (2008) asked whether mixing helps people learn a category. University of California, Los Angeles undergraduates saw six landscapes by each of 12 little-known artists, three seconds each, grouped by artist or interleaved with other artists' work. The test showed new paintings and asked who painted each.

In the test's first block, interleaved artists were named correctly 61% of the time against 35% for grouped ones (120 students, each seeing both); in separate groups of 36 the figures were 59% and 36%. Yet 78% did better with interleaving while 78% judged grouping as good or better. The limits: the test came almost at once, the students came from one university, and the authors could not separate interleaving from spacing.

Rohrer et al. (2020): 54 classrooms

Rohrer et al. (2020) ran a preregistered randomised trial in a Florida school district in 2017 to 2018: 54 seventh-grade maths classes, 15 teachers, 787 students analysed. Over about four months each class did eight worksheets, mostly interleaved or mostly blocked, then all did the same interleaved review. A month later came an unannounced test.

Interleaved classes scored 61% against 38% (d = 0.83), and the effect was positive for all 15 teachers. The authors' caveats: interleaved problems probably take longer, and time was not measured; the gain may be smaller on a test soon after practice; some blocked practice may be needed when a skill is new; and every study so far gave students the answers afterwards.

Brunmair and Richter (2019): where it helps and where it does not

Brunmair and Richter (2019) pooled 59 studies, 238 effect sizes from 158 samples, leaving out motor skills such as sport. The overall benefit was moderate (g = 0.42). By material:

• Paintings: the largest effect (g = 0.67), with other visual material also strong.
• Mathematics: small on average (g = 0.34), though single studies such as Rohrer and Taylor's were very large.
• Expository texts: no significant effect.
• Word lists: blocking was better (g = -0.39), from few studies.

Interleaving helped more when the categories looked alike and the examples within one varied. In 17 studies that tested it, the benefit appeared only when items came back to back (g = 0.73), not when time separated them. Correcting for possibly missing studies lowered the overall estimate to g = 0.29. The authors advise caution with texts and words.

Why does blocked practice feel better? Desirable difficulties

Blocked practice feels better because it produces fast, smooth performance, which people mistake for learning. Bjork and Bjork (2011) separate the two: performance is what you see while studying, learning is the lasting change, and the first is a poor guide to the second. They list interleaving among "desirable difficulties", with spacing, testing and varying the conditions of study, which slow apparent progress and improve later retention.

"Desirable" carries a condition. Bjork and Bjork (2020), who trace the term to 1994, repeat that a difficulty becomes undesirable when the learner lacks the background to respond to it. A mixed set you cannot attempt teaches little.

Blocked vs interleaved practice: which should you use when?

Use blocked practice when a method is brand new, and switch to interleaved practice once you can do each kind on its own. The evidence for that order is indirect: Rohrer et al. (2020) note that almost every maths study gave some blocked practice first, and Pan et al. (2019) found no gain from interleaving Spanish tenses within a single first session.

What do university learning pages advise?

University learning pages agree that mixing helps but differ on how finely to mix, whether topics must be related, and when to start. We read four on 27 September 2026.

• Cornell University describes switching between related skills for short periods, and adds that studying across courses stops you falling behind in others (Cornell University Learning Strategies Center, n.d.).
• Kansas State University suggests two to four topics, each for one or two 25-minute Pomodoro intervals, topics with "natural connections", once each is familiar (Kansas State University Academic Achievement Center, 2026).
• The University of Exeter says to interleave related subjects in one session, such as the cardiovascular and nervous systems (University of Exeter, 2026).
• The University of Arizona allows the same or different subjects, notes that some experts favour related ones, and warns against switching to escape a topic that has become hard (University of Arizona Academic Affairs, n.d.).

Where they differ, the research sides with the narrower version: the studies mixed single problems, back to back, within one subject. Switching between unrelated courses every half hour mostly adds spacing: useful, but not what the interleaving trials tested.

How do you interleave in maths, sciences, languages and essay subjects?

You interleave by mixing kinds of question that could be confused, one at a time, and checking each answer. The evidence is strongest for maths and weakest for essays.

Mathematics

Mixed practice in maths means you see the problem before you know its method. Rohrer et al. (2020) give look-alike pairs, such as a segment's length (Pythagoras) and its slope (rise over run) from the same two points. Our example: take ten questions from four chapters of a statistics module (paired t-test, independent t-test, chi-square, correlation), shuffle them, hide the headings, and name the test before solving each.

Sciences

Samani and Pan (2021) studied 350 students in two sections of a University of California, Los Angeles physics course for life-sciences majors. Each section had four weeks of blocked homework and four of interleaved. On surprise tests one to three weeks later, interleaving raised median scores by 50% and 125% in the two halves, though students rated it harder and thought they had learned less. Midterm scores did not differ, and the authors do not know whether the gain survives cramming. Our example for biology: mixed images of cell types or tissues, named before you check.

Languages

For grammar, interleaving helped only with more practice. Pan et al. (2019) taught University of California, San Diego undergraduates with no Spanish two past tenses. In one session, interleaving gave no benefit; across two weekly sessions it did, 64% against 52% on a test a week later, and 49% against 30% in a second such experiment. Word lists point the other way, so learn vocabulary with spaced flashcards and save mixing for forms you confuse.

Essay subjects

The evidence for essay subjects is thin: we found no study of interleaving and essay writing, and expository texts showed no significant effect in the meta-analysis. What remains is the part of an essay subject that is category learning. Our untested suggestions: in history, decide which historian's interpretation an unlabelled extract reflects; in law, name the doctrine a mixed problem question needs; in psychology or nursing, name the condition in mixed case descriptions.

How do you run a mixed practice session?

A mixed practice session shuffles material you can already do, one kind at a time, with the labels removed. The steps are our own reading of the trials; nobody has tested the sequence as a whole.

1. Learn each new method with a few blocked problems first, until you can do it with notes closed.
2. Pick three or four kinds of question that are easy to confuse, within one subject.
3. Shuffle them so no two in a row are the same kind, and hide the chapter titles.
4. Before solving, write which method or category it is. That choice is what interleaving trains.
5. Check every answer and the choice of method; every maths trial gave feedback.
6. Expect lower practice scores than blocked work gives you. Rohrer and Taylor's mixers practised at 60% and still won the test.
7. Repeat the mixed set on another day, adding older topics as the course grows.
8. For essays, find the evidence as you go. Search EdCitation's Find sources by the claim you need and build each reference in Cite a source.

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Find the studies behind a claim

Find sources covers about 300 million published works; type a topic, or the claim you want support for, and narrow by kind of source, years or open access. On 27 September 2026, "interleaved practice mathematics" returned 32,823 works from OpenAlex. First was Rohrer, Dedrick and Stershic's "Interleaved practice improves mathematics learning." in the Journal of Educational Psychology, listed as 2014 and cited 168 times; the 2020 trial came third, listed as 2019, the year it appeared online. The seventh was a 1998 engineering paper on bit-interleaved coded modulation, so add your subject's words.

Cite it in six styles

Cite a source takes a DOI, a title, a PubMed ID, an ISBN or a link, screens the source for retraction, and sets the entry in any of six styles: APA 7, MLA 9, Chicago 18 author-date, Harvard, IEEE and Vancouver. From 10.1037/edu0000367 it returned, correct as it stands:

Rohrer, D., Dedrick, R. F., Hartwig, M. K., & Cheung, C.-N. (2020). A randomized controlled trial of interleaved mathematics practice. Journal of Educational Psychology, 112(1), 40–52. https://doi.org/10.1037/edu0000367

Cite a source set Kornell and Bjork's title in sentence case, as APA 7 asks, with only the first word, the first word after the colon and proper nouns capitalised (why, and the exceptions).

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Verify references looks up each entry of a pasted list or a whole paper and flags retractions; an entry it could not check is labelled that way, never as "not found". Of this guide's 12 references, 11 were verified and nothing was doubtful, missing or retracted. The twelfth, the Bjork chapter, came back unchecked because its link is a PDF, with the advice to compare the file's title with the entry; we opened the file and the title is the same.

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Quick questions

Is interleaving the same as spaced repetition?

Interleaving and spaced repetition differ: spacing puts time between sessions on one topic, while interleaving mixes kinds of problem within a session. Mixing spaces each kind automatically, which Rohrer et al. (2020) count as part of its benefit.

Does interleaving work for every subject?

Interleaving does not work for everything. Brunmair and Richter (2019) found the largest benefit for paintings and other visual categories, a small one in maths, none for expository texts, and a disadvantage for word lists.

Why does interleaved practice feel harder?

Interleaved practice feels harder because you must choose the method each time, so practice scores drop. Bjork and Bjork call this a desirable difficulty.

Should I mix different subjects in one study session?

Mixing different subjects adds spacing, but the interleaving studies mixed similar problems within one subject, so mix within a subject for the interleaving benefit.

How do I check a study technique's research myself?

Put the technique and your subject into EdCitation's Find sources, for example "interleaved practice physics", read the studies it lists, and paste your chosen references into Verify references before citing them.

References

• Bjork, E. L., & Bjork, R. A. (2011). Making things hard on yourself, but in a good way: Creating desirable difficulties to enhance learning. In M. A. Gernsbacher, R. W. Pew, L. M. Hough, & J. R. Pomerantz (Eds.), Psychology and the real world: Essays illustrating fundamental contributions to society (pp. 56–64). Worth Publishers. https://bjorklab.psych.ucla.edu/wp-content/uploads/sites/13/2016/04/EBjork_RBjork_2011.pdf
• Bjork, R. A., & Bjork, E. L. (2020). Desirable difficulties in theory and practice. Journal of Applied Research in Memory and Cognition, 9(4), 475–479. https://doi.org/10.1016/j.jarmac.2020.09.003
• Brunmair, M., & Richter, T. (2019). Similarity matters: A meta-analysis of interleaved learning and its moderators. Psychological Bulletin, 145(11), 1029–1052. https://doi.org/10.1037/bul0000209
• Cornell University Learning Strategies Center. (n.d.). Effective study strategies. Retrieved September 27, 2026, from https://lsc.cornell.edu/how-to-study/studying-for-and-taking-exams/effective-study-strategies/
• Kansas State University Academic Achievement Center. (2026, March 4). Interleaving technique. Retrieved September 27, 2026, from https://www.k-state.edu/aac/success-tools/collection/interleaving.html
• Kornell, N., & Bjork, R. A. (2008). Learning concepts and categories: Is spacing the "enemy of induction"? Psychological Science, 19(6), 585–592. https://doi.org/10.1111/j.1467-9280.2008.02127.x
• Pan, S. C., Tajran, J., Lovelett, J., Osuna, J., & Rickard, T. C. (2019). Does interleaved practice enhance foreign language learning? The effects of training schedule on Spanish verb conjugation skills. Journal of Educational Psychology, 111(7), 1172–1188. https://doi.org/10.1037/edu0000336
• Rohrer, D., Dedrick, R. F., Hartwig, M. K., & Cheung, C.-N. (2020). A randomized controlled trial of interleaved mathematics practice. Journal of Educational Psychology, 112(1), 40–52. https://doi.org/10.1037/edu0000367
• Rohrer, D., & Taylor, K. (2007). The shuffling of mathematics problems improves learning. Instructional Science, 35(6), 481–498. https://doi.org/10.1007/s11251-007-9015-8
• Samani, J., & Pan, S. C. (2021). Interleaved practice enhances memory and problem-solving ability in undergraduate physics. npj Science of Learning, 6, Article 32. https://doi.org/10.1038/s41539-021-00110-x
• University of Arizona Academic Affairs. (n.d.). L2L strategy: Interleaving. Retrieved September 27, 2026, from https://academicaffairs.arizona.edu/l2l-strategy-interleaving
• University of Exeter. (2026, September 4). How to revise well. Exam Revision. Retrieved September 27, 2026, from https://libguides.exeter.ac.uk/c.php?g=734507&p=5363557