Interleaving is the process of alternating between concepts during learning by periodically returning to earlier ones. Studies have shown that interleaving content promotes retention (Richland et al., 2005; Rohrer, 2012; Rohrer et al., 2015). Rohrer suggests that this is because interleaving helps students distinguish between similar concepts.
Interestingly, Goode and Magill (1986) found that a random selection of topics had the highest impact on learning. Instead of going through the topics sequentially in the standard order (i.e., 1, 2, 3, 4, 5, etc.), going through them in a random order that includes repetition (i.e., 2, 1, 3, 2, 3, 1, 4, 3, 2) was found to produce better learning outcomes. But interleaving seems to have the greatest impact when the concepts being interleaved are similar instead of switching between vastly different topics such as economics, literature, and physiology (Yan & Sana, 2021).
As a result, I encourage my students to use interleaving when studying. I explain the practice (and other study tips, such as retrieval practice and spaced practice) at the beginning of my courses and return to it throughout the semester to reinforce its value. For instance, students learning a subject such as anatomy may develop flash cards on each new system as they cover it in a course. But instead of just practicing on the new cards, they add the new flash cards to their existing stack so that they are always returning to the prior topics while studying.
I have also started to use interleaving in my course design. Standard course design often uses a blocked approach. An instructor teaches about one topic for a few weeks, students take a test on it, then the instructor teaches on a new topic for a few weeks, students take a test on it, and at the end of the course there is a final that covers all the course material. Instead, I return to prior topics throughout my courses.
One class I teach is Introduction to Research Methods. In this course we discuss qualitative, quantitative, and mixed methods. When I have taught each method as a distinct unit, I find that students learn, but not always at the level I wish. Now I alternate between topics, returning to earlier ones to interleave new material with old. For instance, I might cover topics in the following way:
Another way to implement interleaving is to teach topics sequentially but assign homework activities that pull from previously taught content so that students are always returning to prior topics (see Rohrer et al., 2015).
If you teach online, you can interleave topics by using different learning management system tools to engage students with prior work in new ways. For instance, students might get readings and videos on a topic at one time and then return to it later in a discussion forum. Below is an example of how I interleave between topics using different tools:
There are a variety of ways to use interleaving in both course design and studying. Faculty can start by adding a few interleaving activities to their courses, measuring the results, and steadily building in more activities to improve learning outcomes.
Goode, S., & Magill, R. A. (1986). Contextual interference effects in learning three badminton serves. Research Quarterly for Exercise and Sport, 57(4), 308–314. https://doi.org/10.1080/02701367.1986.10608091
Richland, L. E., Bjork, R. A., Finley, J. R., & Linn, M. C. (2005). Linking cognitive science to education: Generation and interleaving effects. In B. G. Bara, L. Barsalou, & M. Bucciarelli (Eds.), Proceedings of the twenty-seventh annual conference of the Cognitive Science Society (pp. 1850–55). Lawrence Erlbaum.
Rohrer, D. (2012). Interleaving helps students distinguish among similar concepts. Educational Psychology Review, 24(3), 355–367. https://doi.org/10.1007/s10648-012-9201-3
Rohrer, D., Dedrick, R. F., & Stershic, S. (2015). Interleaved practice improves mathematics learning. Journal of Educational Psychology, 107(3), 900–908. https://doi.org/10.1037/edu0000001
Yan, V. X., & Sana, F. (2021). Does the interleaving effect extend to unrelated concepts? Learners’ beliefs versus empirical evidence. Journal of Educational Psychology, 113(1), 125–137. https://doi.org/10.1037/edu0000470
Lauren Hays, PhD, is an assistant professor of instructional technology at the University of Central Missouri.