Are spacing and interleaving the same thing?

Are spacing and interleaving the same thing?

A growing body of research has highlighted spacing and interleaving as two of the best learning strategies a student can use for memory retention. Due to their vital role in exam success, a rising number of students and teachers are keen to implement these strategies into their revision or classroom.

However, as students try to come to grips with their understanding of these strategies, scientific research into interleaving and spacing continues to expand. This can result in some confusion, with many in education wondering if spacing and interleaving are just the same thing.

The short answer is no. For a more detailed answer, we went through the research to help you understand the differences between spacing and interleaving, how each of them works and when to implement them.

What is spacing?

Spacing consists of spreading out your revision over a period of time instead of cramming your learning into a single revision session. Essentially, doing a little but often instead of a lot at once. In some studies, using spacing instead of cramming has resulted in a 10% to 30% difference in final test results.

The reason this technique is so effective is because it provides an opportunity for students to forget the material and relearn it, strengthening connections in their long-term memory.

What is interleaving?

Interleaving involves mixing up revision topics instead of focusing on the same one for hours at a time (which is known as “blocking”). It can be used across almost all subjects.

Research shows that implementing interleaving benefits students’ learning by both requiring them to access previous knowledge and helping them make links between different topics, leading to enhanced recall. One study showed that students performed 7% better in their final exam when interleaving their revision compared to those who blocked their revision.

How are spacing and interleaving different?

You would be forgiven for thinking, at first glance, that spacing and interleaving are the same thing: both involve leaving gaps between revision sessions on a given topic to make stronger connections.

However, if you look a bit closer, you’ll realise that the two study techniques are a lot more different than it seems.

Use of time

One of the main differences lies in their concepts of time. Spacing focuses on longer periods of time: for example, doing a given amount of revision over the course of two weeks rather than cramming it all in one evening. On the other hand, interleaving concerns shorter periods of time: it’s about alternating between topics during one study session.

Benefits to memory

Research shows that spacing your learning enhances memory because constantly referring back to material and relearning it is more effective over a longer timeframe. As mentioned earlier, this is because it actually gives you enough time to almost forget it. In contrast, interleaving enhances inductive learning (which is when students observe and examine examples of a theory to discover the patterns between them, working out the rules or principles of the theory themselves) and later memory retrieval.

Choices of topics

To use either of these techniques effectively, it is vital to understand this difference. When using spacing, the topics or subjects you revise don’t particularly have an impact on the results. But in order to experience the benefits of interleaving, the topics you mix up should be related or similar.

Research shows that when interleaving completely unrelated topics, there is no benefit on memory retention. In practice, this could mean alternating between different John Keats poems for English to establish common themes rather than mixing maths revision with religious studies.

Are interleaving and spacing related?

As you now know, spacing occurs between revision sessions, whilst interleaving occurs within sessions. The result is that interleaving topics in your revision session will mean that you won’t cover the entire topic in one session. This causes you to revisit the topic at a later date so you can continue your learning, resulting in spacing. This is a classic square/rectangle effect: all interleaving is spacing, but not all spacing is interleaving.

Another interesting point is that, although both revision strategies lead to slower and more error-prone learning in the short-term, they boost memory retention when implemented over a longer time span. So, these may frustrate students at first, but if they stick to it, it will pay off.

How to use these effective revision strategies

How to use spacing

One study found that students who spaced out their revision sessions got an average mark of 74% in the final test, as opposed to a 49% average for those who crammed theirs - making it a very attractive technique for students.

An easy way to implement spacing is to create a study schedule both at a weekly and monthly basis. For example, at a weekly level, you could study History on a Monday then revisit what you learnt on Thursday. Then, at a monthly level, you can decide how much revision to do on one topic per week based on how far the test is. Research shows that there may be an optimum gap to leave depending on when you’ll need to retrieve the information. The researchers found the following timeline offers good guideline:

How Far Away The Test Is

7 Days

35 Days

70 Days

350 Days

Gap Between Revision Sessions

3 Days

8 Days

12 Days

27 Days


How to use interleaving

As mentioned earlier, interleaving is more efficient when the mixed topics are related. For example, when studying biology, you can alternate between evolution and inheritance instead of focusing on evolution alone. Here’s what it looks like:

blocking v interleaving

However, this isn’t a cure-all and it’s important to know when to use this strategy or not. Our blog “Blocking or interleaving: which is better for revision?” Takes a deeper look at this question.

Final Thoughts

Spacing and Interleaving are both highly effective revision techniques that can help students learn more efficiently, improve memory retention in the long-term, and result in better academic performance.

However, for the strategies to be effective, they must be used correctly. As a result, eliminating the common misconception that they are the same is a good place to start. Don’t forget:

  • They have different concepts of time as spacing is about between session spacing of topics whilst interleaving is about within session spacing of topics.
  • Spacing benefits memory recall whilst interleaving enhances inductive learning and later memory retrieval.
  • Interleaving requires similarity between topics whereas spacing doesn’t.

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