Interleaving Really Works

We’ve known for quite a while that certain approaches to study, though seemingly more difficult (they’re not) and also thought of by students as less effective (they’re not) really help learning, retention, and even transfer. These, so-called desirable difficulties (Bjork, 1994), include approaches such as retrieval practice (also called by some no-stakes testing or self-testing), spaced practice, elaboration, and interleaving (also known as variability of practice; Van Merrienboer & Kirschner, 2018).

Variability of Practice
Organizing learning tasks in such a way that they differ from each other on dimensions that also differ in the real world (e.g., the situation or context, the way of presenting the task, the saliency of defining characteristics). Variability has positive effects on inductive learning and transfer.

In a recent preregistered study on interleaving entitled Interleaved practice enhances memory and problem-solving ability in undergraduate physics, Joshua Samani and Steven C. Pan investigated whether continuously alternating between topics during practice, or interleaved practice, improves memory and the ability to solve problems in undergraduate physics. They found that over a period of 8 weeks, 350 students in two lecture sections of a university-level introductory physics course completed thrice-weekly homework assignments, each containing problems that were interleaved (i.e., alternating topics) or conventionally arranged (i.e., one topic practiced at a time).

On two surprise criterial tests containing novel and more challenging problems, students recalled more relevant information and more frequently produced correct solutions after having engaged in interleaved practice (with observed median improvements of 50% on test 1 and 125% on test 2).

Despite benefiting more from interleaved practice, students tended to rate the technique as more difficult and incorrectly believed that they learned less from it. This is often the case with desirable difficulties. Metacognitive judgements are often diametrically opposed to the actual results! This means that we need to do more to help students ‘experience’ their benefits. Thus, in a domain that entails considerable amounts of problem-solving, replacing conventionally arranged with interleaved homework can (despite perceptions to the contrary) foster longer lasting and more generalizable learning.

The authors write:

From the perspective of undergraduate physics education and other forms of STEM learning, the present results serve as a proof-of-concept for a relatively low-cost learning intervention (in terms of time required and necessary equipment) that has the potential to yield sizeable learning benefits. The finding that interleaving benefits learning for one of the most challenging subjects that college students have to master, and does so for the case of relatively difficult problem-solving materials, invites a re-evaluation of conventional instructional approaches and a greater appreciation for the influence of practice schedules in the development of skills and expertise. Indeed, it is becoming increasingly apparent that there are a variety of educationally authentic contexts in which human learners benefit more from practicing multiple topics from a given domain at one time, rather than practicing one topic at one time.

Bjork, R. A. (1994b). 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.

Bjork, R. A. (1994a). Institutional impediments to effective training. In D. Druckman and R. A. Bjork (Eds.), Learning, remembering, believing: enhancing individual and team performance. (pp.295-306). National Academy Press.

Samani, J., Pan, S. C. (2021). Interleaved practice enhances memory and problem-solving ability in undergraduate physics. npj Sci. Learn. 6, 32.

Van Merriënboer, J. J. G., & Kirschner, P. A. (2018). Ten steps to complex learning (Third edition). Routledge.