Research School Network: All Mixed Up Does ​‘mixing up topics’ explain what interleaving means?

All Mixed Up

Does ​‘mixing up topics’ explain what interleaving means?

by Kingsbridge Research School
on the

Like retrieval practice and spaced practice, interleaving is a strategy that helps students remember what they study. Unlike retrieval practice and spaced practice, it is perhaps more prone to oversimplification. Often, for example, interleaving is described as mixing up topics’. While this is partly true, it might well lead us to ignore the nuances that make interleaving effective.

What is interleaving?

If we study several examples of an idea or problem in a study session, we call that blocked practice. A lesson on the use of semicolons that features a teacher explanation followed by a series of semicolon-based problems would be an example of blocked practice.

Interleaving, on the other hand, means we study different ideas or problems within a single study session. If we have been taught how to use semicolons, colons and commas in separate lessons (blocked practice), and then practice all three within a single study session, then we are interleaving. We might solve one problem featuring semicolons, then move on to one featuring colons, then another on commas, then back to semicolons, and so on.

Notice that each session features punctuation. Interleaving appears to work best when the things we’re studying are related. It is less effective when we mix up unrelated content or content from entirely different subjects.

Where has it shown promise?

A study by Rohrer and Taylor (2007) contrasted blocked practice and interleaving by having students study related maths problems. They were given a prism and had to calculate the total number of faces, corners, edges, or angles. Doing so required them to use one of four particular formulas.

One group did this using blocked practice, the other interleaving. Although the interleaving group performed worse during practice sessions, they outperformed the blocked practice group on a subsequent test (significantly – a 78% test score compared to 38%). Impaired performance during the practice sessions is explained by desirable difficulty’: the additional difficulty imposed by having to select the right formula proves to be worthwhile when it comes to remembering the different formulas.

One problem with claims about interleaving is that, because practice is necessarily spread over time, the supposed benefits might be due to spaced practice rather than interleaving. The study by Rohrer and Taylor (2007) tried to control for this by equally spacing practice sessions for both the blocked practice group and the interleaving group.

When to use interleaving

1. To improve discrimination between related concepts:

One explanation claims that interleaving is beneficial because it requires students to discriminate between similar ideas or problems, as in the maths example. Another study by Kornell and Bjork (2008) had an interleaving group see paintings by a variety of artists while the blocked practice group studied artists one at a time. Again, the interleaving group’s improved ability to recognise styles is explained by the discriminative-contrast hypothesis’. By switching between similar problems, we improve our perception of the differences. The benefits of interleaving have been found even when taking into account differences in participants’ working memory capacities, (Sana et al., 2018).

2. To help students select strategies

As well as helping us to perceive the critical attributes of related concepts, interleaving also helps us select the right tools for the job. If we interleave related formulas – the equations of motion in physics, for example – we help students learn not only the individual formulas, but when to select each one. Since part of metacognition involves selecting appropriate strategies to solve problems, interleaving may be a useful way to facilitate this.

3. To improve learning by interleaving testing and worked examples

Another way that interleaving appears to support learning is when we use it to alternate between solving a problem and seeing a worked example (if P represents a problem and E a worked example, we are structuring a lesson like this EPEPEP instead of like this: EEEPPP).Doing so seems to increase recall of the particular strategy students are learning and, like the discrimination example above, offers more opportunities for discriminating between the model example and one’s own efforts.

It’s worth considering whether what interleaving achieves in all of these cases is what Engelmann called continuous conversion’, when we change one example into the next example without any interruption of any sort’ (Engelmann and Carnine, 1982, p.34). In other words, by interleaving examples and non-examples, we help learners perceive concepts with greater clarity.


Think of interleaving as:

- an alternative to blocked practice
- a way to help students distinguish between related concepts or examples and non-examples
- a way to help students learn when to select particular tools or strategies
- a way to facilitate checking answers against worked examples

Don’t think of it simply as mixing up topics’

Distinguish between spaced practice and interleaving


Rohrer, D., & Taylor, K. (2007). The shuffling of mathematics problems improves learning. Instructional Science, 35, 481 – 498.

Kornell, N., & Bjork, R. A. (2008). Learning concepts and categories is spacing the enemy of induction”? Psychological Science, 19, 585 – 592.

Sana, F., Yan, V., Kim, J., Bjork, E. and Bjork, R. (2018). Does Working Memory Capacity Moderate the Interleaving Benefit?. Journal of Applied Research in Memory and Cognition, 7(3), pp.361 – 369.

Engelmann and Carnine (1982) Theory of instruction: principles and applications. Eugene, OR: NIFDI Press

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