Evidence for Desirable difficulties: why easy learning fails #

Every substantive claim on the Desirable difficulties: why easy learning fails 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 · strong evidence — Conditions that make learning feel harder and slower in the moment (desirable difficulties) tend to produce more durable and flexible long-term learning.

The desirable-difficulties framework remains a well-established and frequently replicated principle in the science of learning; large reviews continue to find that spacing, retrieval practice, interleaving and variation reliably improve long-term retention despite depressing in-session performance.

Sources: Dunlosky, Rawson, Marsh, Nathan & Willingham (2013), Improving Students’ Learning With Effective Learning Techniques, Psychological Science in the Public Interest — https://journals.sagepub.com/doi/10.1177/1529100612453266 · Bjork & Bjork (2011), Making things hard on yourself, but in a good way — https://bjorklab.psych.ucla.edu/wp-content/uploads/sites/13/2016/04/EBjork_RBjork_2011.pdf · full reference ›

Supported · strong evidence — Performance during practice and durable learning are distinct, and conditions can improve one while harming the other, so in-session performance is an unreliable index of learning.

Soderstrom & Bjork’s distinction between performance and learning is a foundational and widely accepted result; many studies show manipulations that boost practice performance leave little durable learning, while others that depress practice performance enhance retention and transfer.

Supported · moderate evidence — Ease of processing (perceptual or processing fluency) feels like knowing but is a poor predictor of later memory, producing illusions of competence.

It is well documented that fluency and familiarity inflate confidence and judgments of learning out of step with actual retention; learners systematically overrate easy, fluent study experiences such as re-reading.

Sources: Koriat & Bjork (2005), Illusions of Competence in Monitoring One’s Knowledge During Study, Journal of Experimental Psychology: LMC — https://bjorklab.psych.ucla.edu/wp-content/uploads/sites/13/2016/07/Koriat_Bjork_2005.pdf · Dunlosky, Rawson, Marsh, Nathan & Willingham (2013), Improving Students’ Learning With Effective Learning Techniques, Psychological Science in the Public Interest — https://journals.sagepub.com/doi/10.1177/1529100612453266 · full reference ›

Supported · strong evidence — Re-reading material is a low-utility study strategy: it feels productive and increases fluency but yields weak durable learning compared with active strategies.

Dunlosky et al.’s comprehensive review rated re-reading as low-utility, and subsequent work consistently shows massed re-reading produces far less durable learning than retrieval practice or spacing despite high subjective fluency.

Supported · strong evidence — Retrieving information from memory (self-testing) produces stronger long-term retention than restudying the same material (the testing effect).

Meta-analyses of hundreds of comparisons find a robust, moderate-to-large testing effect: practising retrieval reliably outperforms restudy on delayed tests across materials and populations.

Sources: Adesope, Trevisan & Sundararajan (2017), Rethinking the Use of Tests: A Meta-Analysis of Practice Testing, Review of Educational Research — https://journals.sagepub.com/doi/10.3102/0034654316689306 · Rowland (2014), The effect of testing versus restudy on retention: A meta-analytic review, Psychological Bulletin — https://doi.org/10.1037/a0037559 · full reference ›

Supported · strong evidence — Spacing study across time, with gaps between sessions, produces more durable retention than massing the same study into a single block.

The spacing effect is one of the most replicated findings in memory research; Cepeda et al.’s meta-analysis and many subsequent studies confirm distributed practice reliably beats massed practice for long-term retention.

Sources: Cepeda, Pashler, Vul, Wixted & Rohrer (2006), Distributed practice in verbal recall tasks: A review and quantitative synthesis, Psychological Bulletin — https://doi.org/10.1037/0033-2909.132.3.354 · full reference ›

Supported · moderate evidence — Interleaving different problem types or topics within a session lowers practice performance but improves later discrimination and choice of the correct method compared with blocked practice.

Meta-analytic evidence supports an interleaving benefit, especially for mathematics and category learning, though the effect size varies with materials and is smaller or null in some domains, so the benefit is real but not universal.

Sources: Brunmair & Richter (2019), Similarity matters: A meta-analysis of interleaved learning and its moderators, Psychological Bulletin — https://doi.org/10.1037/bul0000209 · Rohrer, Dedrick & Stershic (2015), Interleaved practice improves mathematics learning, Journal of Educational Psychology — https://doi.org/10.1037/edu0000001 · full reference ›

Supported · moderate evidence — Practising a skill under varied conditions rather than identical repetitions improves transfer of learning to new situations, even if it depresses performance during acquisition.

Variability-of-practice and contextual-interference research generally shows varied practice enhances generalisation and transfer relative to constant practice, with the trade-off of poorer acquisition-phase performance; effects are reliable though moderated by task and learner.

Sources: Soderstrom & Bjork (2015), Learning Versus Performance: An Integrative Review, Perspectives on Psychological Science — https://journals.sagepub.com/doi/10.1177/1745691615569000 · Czyz (2021), Variability of Practice, Information Processing, and Decision Making—How Much Do We Know?, Frontiers in Psychology — https://www.frontiersin.org/articles/10.3389/fpsyg.2021.639131/full · full reference ›

Supported · moderate evidence — A difficulty only aids learning when the learner can successfully meet it; difficulties that exceed the learner’s resources and yield no meaningful processing do not help.

The Bjorks explicitly bound the principle: a difficulty is desirable only if the learner has the background and effort to overcome it, and otherwise becomes an undesirable difficulty—a qualification widely echoed in the instructional-design literature.

Sources: Bjork & Bjork (2011), Making things hard on yourself, but in a good way — https://bjorklab.psych.ucla.edu/wp-content/uploads/sites/13/2016/04/EBjork_RBjork_2011.pdf · full reference ›