I’ve been reading research and writing about it on this website for around eight years. I’ve written numerous times on learning strategies such as retrieval practice, spaced practice, dual coding, and much, much more. But, one strategy that has never featured on any article I’ve written is interleaving. Go ahead, do a keyword search for it here. There may be an article where it is mentioned, but I’ve never looked at any research and considered how to use it appropriately in my classes. Why, you might ask, have I never written about interleaving? Well…mostly because it can be particularly difficult to do correctly (and well) in class. It is so nuanced and the research can be so varied. It’s really tough to nail down a somewhat standard and applicable way to interleave. And that makes it very difficult to make it widely applicable for teachers.
But the interleaving drought ends today. : )
I’ve found an article on the subject that I just love. And what I mean by that is (1) its experimental design is simple ,(2) it is easily understood for the non-researcher reader, and (3) it is easily applicable for a wide range of teachers in a wide range of classrooms with a wide range of students. To me, that’s the trifecta for a research article. And it is quite rare.
Another aspect of this study that I really like is that I believe it does a better job of isolating the impact of interleaving. Most studies on the topic also involve spacing out the practice with the interleaving, which makes results somewhat confounding. Is it the interleaving practice or the spacing practice that is producing the positive results? This study keeps it simple and reduces the spaced practice.
So, let’s get into it. First of all, what is interleaving?
“Practicing problems (1, 2, 3) of related concepts (A, B, C) in a mixed-up order (A1C1B1C2B2A2B3C3A3).” (1)
This is in contrast to the more popular blocked practice of problems. Using the same pattern as above, blocked practice would look something like (A1A2A3B1B2B3C1C2C3).
In more practical terms, blocking practice means asking a group of questions about a specific topic from class before moving on to questions about another topic in class. So, if I blocked my questions on the material covered in my class yesterday, I would first pose questions about Gestalt principles of perception (A) before asking about binocular and monocular depth cues (B) and then finish up with questions about schemas, assimilation, and accommodation (C). This is a very popular method for reviewing topics in class, on homework, or via some form of study guide. I use it often in my classes.
Interleaving practice says to split those topics up and ask a question or two about one topic before questioning about another topic and maybe another. Then return to the original concept and ask about it again before moving on to the other material again. While this may seem a little counterintuitive and will probably be a bit more cognitively challenging for students, there is evidence that it produces better learning outcomes long-term.
In the current study, 155 9th-12th grade students were given end of week practice quizzes for 4 weeks. Concepts would be assigned to a practice or non-practice condition. The information in the non-practice condition would not appear on any end of week quiz and only appeared on the final test one month after the final quiz. The information assigned to the practice condition would either be quizzed via blocked or interleaved questioning. This would alternate from week to week, meaning students would take two end of week quizzes that utilized blocked questioning and two that would utilize interleaved questioning.
One month after the final quiz, students were given a final test composed of questions from the blocked quizzes, questions from the interleaved quizzes, and questions from material assigned to the non-practice condition.
The results?
In general, students actually performed worse on the end of week quizzes that utilized interleaved practice versus blocked practice. I think this speaks to the increased cognitive demand of changing topics.
But, when we look at the final test given a month later, in every instance, students performed better on the questions that were interleaved. No matter the grade the student was in or what science class they were taking, they performed better on the interleaved items than the blocked and non-practice items. And, of course, information that was reviewed via blocked practice outperformed material from the non-practice condition…adding to the century of research demonstrating the positive impact of retrieval practice. Another way of thinking about it is that some practice is almost always going to be better than no practice, but some methods of practice are better than others.***
Pretty impressive, if you ask me. Overall, Interleaved practice > Blocked practice > Non-practice. That is super interesting…but my nerdy self wants to know why. Why does interleaving seem to work better than blocked practice?
A leading belief posits that when concepts are interleaved, students are more likely to notice the features that discriminate between concepts (2)…a bit like non-examples. When students can more clearly see what a concept isn’t, that can also help them to see what it is. In contrast, when concepts are blocked, there are fewer chances to notice the sometimes important features that may distinguish one bit of material from another.
I quickly want to come back to how befitting this study on interleaving is to the classroom teacher. Most interleaving studies involve a more complex manner of spacing out the topics and that doesn’t usually equate to an easily applicable concept for teachers in the real classroom. This study kept it quite simple and teachers can actually pretty easily accommodate for their specific subject, students, and time constraints.
Love this. Thank you, researchers. : )
So, now I’m off to think about specific concepts that I know students find more difficult to understand or seem more confusing to add to my regular retrieval practice to begin my classes.
How do you think you can use this in your classroom?
What subtle, or perhaps maybe not so subtle, changes would you make for your students?
***Similarly, I’ve been stating it to my students like this: some exercise is always better than no exercise, but there are specific types of exercise (weight lifting, interval training sessions, etc.) that can make you faster/stronger more efficiently and effectively than others. Students don’t seem to think about the need to study like the need to practice a dance routine or an instrument in order to improve. More on this discussion I have with my students here.
If you’d like more information on topics of memory, attention, and learning strategies to create a more effective classroom…boy do I have the book for you. Okay, so I’m a little biased because I wrote it. : ) It’s called Do I Have Your Attention? Understanding Memory Constraints and Maximizing Learning. If you access this link, you can find more information on the book, endorsements from Dr. John Hattie, Dr. John Sweller, Dr. Dan Willinham, and more, and methods to order in both the US and UK.
I have also presented at many conferences and to many faculties on these topics. If you are interested in collaborating, don’t hesitate to reach out. You can find me on Twitter, Bluesky, or feel free to contact me through my website.
- Sana, F., & Yan, V. X. (2022). Interleaving retrieval practice promotes science learning. Psychological Science, 33(5), 782-788.
- Carvalho, P. F., & Goldstone, R. L. (2017). The sequence of study changes what information is attended to, encoded, and remembered during category learning. Journal of Experimental Psychology: Learning, Memory, and Cognition, 43(11), 1699.
Feature image by Pavel Danilyuk: https://www.pexels.com/photo/children-sitting-at-the-table-8423051/