Evidence for Interleaving: mix up what you practise #

Every substantive claim on the Interleaving: mix up what you practise page is checked against current research. Here is each claim, how well today’s evidence supports it, and the sources. The full, de-duplicated source list lives on the references page.

Supported · moderate evidence — Interleaving different problem types within a practice set (ABCABC) produces better performance on a later test than blocking the same problems by type (AAABBB), even though it lowers performance during practice.

Rohrer & Taylor’s mathematics experiments showed mixed practice depressed acquisition but markedly improved delayed test scores, and this pattern has been replicated in subsequent classroom and lab studies of maths and category learning.

Sources: Rohrer & Taylor (2007), The shuffling of mathematics problems improves learning, Instructional Science — https://doi.org/10.1007/s11251-007-9015-8 · Rohrer, Dedrick & Stershic (2015), Interleaved practice improves mathematics learning, Journal of Educational Psychology — https://doi.org/10.1037/edu0000001 · full reference ›

Mixed · moderate evidence — The benefit of interleaving over blocking is real but conditional: it depends strongly on the materials, being substantial in some domains and small or absent in others.

Brunmair & Richter’s meta-analysis of 59 studies found an overall medium interleaving benefit but with large heterogeneity strongly moderated by stimulus type, so the effect is well-supported in aggregate yet not uniform across tasks. Genuinely contested at the level of where and how large the effect is, not whether it exists.

Sources: Brunmair & Richter (2019), Similarity matters: A meta-analysis of interleaved learning and its moderators, Psychological Bulletin — https://doi.org/10.1037/bul0000209 · full reference ›

Supported · moderate evidence — Interleaving helps most when the interleaved items are similar and confusable, because mixing them forces the learner to discriminate the features that distinguish the categories.

The meta-analysis identified stimulus similarity as a key moderator, with the largest interleaving advantages for confusable categories, consistent with a discriminative-contrast account; benefits shrink when items are dissimilar or unrelated.

Sources: Brunmair & Richter (2019), Similarity matters: A meta-analysis of interleaved learning and its moderators, Psychological Bulletin — https://doi.org/10.1037/bul0000209 · Kornell & Bjork (2008), Learning concepts and categories: Is spacing the enemy of induction?, Psychological Science — https://doi.org/10.1111/j.1467-9280.2008.02127.x · full reference ›

Supported · moderate evidence — Interleaving improves the ability to identify which type of problem one is facing and select the correct method, a discrimination skill that blocked practice trains poorly.

Analyses of interleaved maths practice attribute much of its advantage to improved problem-type discrimination—learners under blocking can apply a procedure without identifying the problem, whereas interleaving requires choosing the strategy, and errors of method selection drop after interleaved practice.

Sources: Rohrer, Dedrick & Stershic (2015), Interleaved practice improves mathematics learning, Journal of Educational Psychology — https://doi.org/10.1037/edu0000001 · Rohrer & Taylor (2007), The shuffling of mathematics problems improves learning, Instructional Science — https://doi.org/10.1007/s11251-007-9015-8 · full reference ›

Supported · strong evidence — Interleaving lowers performance during practice while improving longer-term retention and transfer, so in-session ease is a misleading guide to its effectiveness.

Interleaving is a canonical desirable difficulty: the learning-versus-performance literature consistently shows it depresses acquisition-phase performance while enhancing delayed retention and transfer relative to blocking.

Supported · moderate evidence — Interleaving in cognitive learning and contextual interference in motor-skill learning reflect the same underlying principle: jumbled, less predictable practice depresses performance during acquisition but improves later retention and transfer.

The contextual-interference effect in motor learning and interleaving in verbal/conceptual learning are widely treated as expressions of one desirable-difficulty mechanism; both reliably trade poorer acquisition for better delayed performance, though magnitudes vary by task and skill level.

Sources: Soderstrom & Bjork (2015), Learning Versus Performance: An Integrative Review, Perspectives on Psychological Science — https://journals.sagepub.com/doi/10.1177/1745691615569000 · Brunmair & Richter (2019), Similarity matters: A meta-analysis of interleaved learning and its moderators, Psychological Bulletin — https://doi.org/10.1037/bul0000209 · full reference ›

Supported · moderate evidence — When the interleaved items are unrelated or dissimilar, interleaving provides little or no advantage over blocking because there is nothing to discriminate between.

Because the interleaving benefit is moderated by stimulus similarity, effects for unrelated or low-similarity materials are small to negligible in the meta-analytic data, which fits the discriminative-contrast explanation for why interleaving works.

Sources: Brunmair & Richter (2019), Similarity matters: A meta-analysis of interleaved learning and its moderators, Psychological Bulletin — https://doi.org/10.1037/bul0000209 · full reference ›