What is interleaving, and why does it work?

Interleaving is an increasingly popular teaching & learning strategy to use. This technique involves studying topics within the same subject by mixing them up, rather than studying each topic separately. Using this strategy can be very effective, with one research paper finding that students who interleave their studies perform nearly twice as well as their peers who use blocking.

And yet, for many teachers, interleaving remains the area of cognitive science that is most confusing. We’ve had a number of teachers reach out to us at InnerDrive and ask us why does interleaving help. So we dug into the research to find out…

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What is interleaving?

Interleaving involves mixing up topics within the same subject when studying. This is the opposite of blocking, which is fully covering one topic before moving on to the next. This graphic gives an example (taken to the nth degree for illustrative purposes only) of the difference between the two:

Blocking vs interleaving graph


Benefits of interleaving

Why should students use this strategy? Although it might be harder to implement at first, using interleaving has been shown to have many benefits including:

  • Improved academic performance – In an interesting study, students who used interleaving performed significantly better than those who revised using blocking.

  • Improved memory – As interleaving encourages students to make connections between topics, it can help strengthen their memory associations. As a result, students can consolidate and retain the information for a longer period of time.

  • Knowing which strategy to use – As interleaving encourages students to compare and contrast between different strategies, it can help them think about the process in more detail. Therefore, when they are solving a new question, they are more likely to find out which strategy is the most effective to use.


Why interleaving works


1. Discrimination Learning: Spotting differences amongst similar things

Researchers use the phrase "discrimination learning" to describe how students need to distinguish between differences between similar topics. For example, this study highlights how for example in Biology students need to learn about “transcription, transduction, transformation and translation – four terms with similar spellings and meanings”.

Interleaving prompts students to think about some of the differences between each topic, as when they do the opposite (i.e. blocking) towards the end they tend to think on autopilot. The seduction of short-term competence can hinder their ability to think critically about the information they are processing.

Likewise, some evidence suggests that highlighting the novelty of information can help positively influence memory. By interleaving, this novelty is more pronounced, which prompts students to think harder, as they are alternating what they are focusing on.

Highlighting the differences during interleaving also helps students to reflect more about what strategy they need to focus on. This is less likely to happen during blocking, as they simply need to repeat the same process over and over again. By doing so, they are more likely to remember it again in the future.

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2. Involves remembering similarities amongst different things

As well as being able to spot the differences between each topic, interleaving also helps students to focus on the similarities that they previously might have not been aware of. There is some research to suggest that similarities “may lead to improve task performance, possibly due to increased stability or precision of the memory representation during maintenance.

These similarities amongst different things can help refine and develop students’ schema. This makes it more nuanced, meaning that there are more accurate "anchor points" to which students can connect new information to already learnt material.


3. Involves the benefits of spacing

Arguably one of the biggest benefits of interleaving is that incorporates another effective learning strategy: spacing.

Spacing involves students spreading out their learning over a period of time instead of cramming it all within one study session. When students interleave their studies, they leave one topic for a period of time before revisiting it later on. Therefore, they also incorporate spacing in their learning.

But why is this useful? Well, one of the main benefits of using spacing is that it gives time for students to forget the topic. Therefore, when they revisit it, they must re-learn the material. This process is key in cementing the information to their long-term memory. Research also shows the benefits of spacing, with students who space their revision scoring higher than those who crammed their studies.

However, one thing to keep in mind is that spacing and interleaving are two different learning strategies. Although all interleaving is spacing, not all spacing is interleaving.

The difference between these two is explored in great detail in this research article (if you are in a hurry and can’t read that full article, it essentially says that spacing relies on resting between learning, which helps replenish cognitive effort, whereas interleaving involves direct contrasting between different topics).

You can read more about this topic in our blog, “Are spacing and interleaving the same thing?”, which we are going to update soon; there have been some really nice developments in the research since we originally wrote it, but there is still some good information in it.

Spacing and interleaving relation graph

A word of warning

Although interleaving is a very helpful learning tool, it might be difficult to implement at first. In a previous study, although students benefitted the most from using interleaving, students tended to rate the technique as more difficult. Surprisingly, students often believed that they also learnt less from it.

Therefore, it is important to not only encourage students to interleave their learning but also highlight the benefits of using it to them, as explained in this blog.


Final Thoughts

Interleaving, which involves mixing up the topics when learning, can be a very effective learning technique, for many reasons which include incorporating spacing and being able to compare and contrast across the different topics (i.e. "discrimination learning").

It can be tricky to use, but if done well, can be a highly effective and efficient way to accelerate learning.


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