Principle 05 · The right effort
Desirable difficulties and interleaving: why mixing topics helps learning stick
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Short answer
Desirable difficulties are conditions that make practice harder in the moment but can improve long-term retention, as long as the learner has the background to overcome them. Interleaving is one of them: a 2021 systematic review found benefits for memory and for transfer to new cases when examples of several concepts are mixed.
What it is
The term desirable difficulties comes from Robert Bjork. It describes practice conditions that seem to make learning slower or harder, but that can improve long-term retention.
Interleaving is one of them: instead of practising one type of problem at a time, in blocks, several types are mixed in the same session.
What the research says
Desirable only if within reach
Robert and Elizabeth Bjork stress that a difficulty is desirable only if the learner has the prior knowledge to respond to it successfully; without that, it becomes an undesirable difficulty. They also point out that performance during practice is not a reliable measure of learning, which can lead learners and teachers to prefer poorer conditions.
Bjork and Bjork (2020), Journal of Applied Research in Memory and Cognition.
Interleaving helps memory and transfer
A systematic review of 26 studies, with a meta-analysis of 17, found interleaving benefits for memory of studied examples (g up to 0.65) and for transfer to new examples (g up to 0.66). The benefit was greatest when the differences between items were subtle, and it held on delayed tests. Most studies were lab studies with university students.
Firth, Rivers and Boyle (2021), Review of Education.
Harder, and better, in a real course
Over eight weeks, students in an introductory physics course did homework with problems that were either interleaved or grouped by topic. On two surprise tests with new and harder problems, interleaved practice led to median improvements of 50% and 125%. Students rated the technique as harder and wrongly believed they learned less from it.
Samani and Pan (2021), npj Science of Learning.
The g value measures the difference between groups in standard deviations: the larger it is, the bigger the advantage for the group that interleaved.
Where the idea comes from. Robert Bjork coined the term in 1994: conditions that make practice more demanding can improve long-term retention. In 2007, Rohrer and Taylor showed that mixing types of mathematics problems during practice greatly improved performance on a test one week later, compared with blocked practice.
Ease in the moment can be misleading. The right effort is what lasts.
Why it works
- It forces a choice. When topics are mixed, repeating the same procedure is not enough: you first have to work out what kind of question you are facing.
- It avoids a false sense of mastery. In blocks, the right answer looks obvious because it matches the previous one.
- It pairs with spacing. Mixing topics naturally spreads out reviews of the same topic, which connects to spaced repetition.
How the game applies it
Which ITIL v5 practice restores service as quickly as possible?
21- Every round mixes questions from earlier levels with new ones.
- The timer and plausible wrong answers add moderate effort to every answer.
- Three helps per round (more time, 50/50 and swap the question) keep a hard question from blocking the round, so the difficulty stays desirable.
References
- Firth, J., Rivers, I. & Boyle, J. (2021). A systematic review of interleaving as a concept learning strategy. Review of Education, 9(2), 642-684. doi:10.1002/rev3.3266
- Samani, J. & Pan, S. C. (2021). Interleaved practice enhances memory and problem-solving ability in undergraduate physics. npj Science of Learning, 6, 32. doi:10.1038/s41539-021-00110-x
- 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. doi:10.1016/j.jarmac.2020.09.003
- Rohrer, D. & Taylor, K. (2007). The shuffling of mathematics problems improves learning. Instructional Science, 35(6), 481-498. doi:10.1007/s11251-007-9015-8
- Bjork, R. A. (1994). Memory and metamemory considerations in the training of human beings. In J. Metcalfe & A. Shimamura (Eds.), Metacognition: knowing about knowing. MIT Press, pp. 185-205.