Interleaving hurts – but that's (partly) why it helps

Interleaving is an increasingly popular learning technique and is shown to potentially help students increase their rate of learning. However, one issue that many teachers encounter when using this technique is that students often dislike it and think that it is ineffective. This often makes them reluctant to use it, making it difficult to implement this strategy in the classroom.

So how can we resolve this issue? Well, let’s first take a look at what interleaving is, what the research shows and some ways to deal with this problem…

What is interleaving?

Interleaving is a learning technique that involves alternating the order of topics within a subject. This is the opposite of blocking, which is when a single topic is covered in full before moving on to the next.

Let’s take Maths as an example to highlight the difference between the two. When students interleave their revision, they might answer questions that include algebra, fractions and multiplications in one study session. However, when blocking their revision, they would focus on fractions exclusively, then on multiplications, and finally, on algebra. The graph below shows how the same amount of time can be spent on an interleaving revision session compared to a blocking session.

What does the research say?

In an interesting study, researchers investigated the benefits of interleaving. To do this, students were given homework assignments for 8 weeks, which either included interleaving or blocking the topics. When interleaving, researchers found that students:

• Reported it as being more difficult
• Perceived fewer learning benefits
• Performed worst compared to the blocking assignments

This might be surprising as it shows that in the short term, interleaving might be worse than blocking. However, the researchers also found another very important difference. When the students were given a surprise test that contained new and more challenging problems, those who took part in an interleaved practice performed much better than those who took part in a blocked practice. Therefore, in the short term, interleaving might be more difficult than blocking - but it pays off in the long term.

So why is interleaving an effective technique? Well, some reasons for this include:

• Compare and contrast – Interleaving helps students focus on the subtle but important differences within a topic as well as similarities, helping them understand the topic better. 
• Improves long-term memory – It encourages students to make connections between topics, which helps strengthen memory associations. Previous research found that interleaving helps consolidate information, resulting in better long-term retention.
  
• Helps students know which strategy to use – Interleaving helps students practise choosing the most effective strategy to use.

What does this mean for a classroom teacher?

Although the long-term benefits of interleaving are clear, it might be more difficult to achieve if students do not like using it. One reason for this is that students might have a metacognitive illusion, which is the tendency to inaccurately judge the process of their learning. This might mean that they believe that they are not achieving much when interleaving, but this is not true.

In another study, researchers who investigated this illusion found that:

• Students have a prior belief that blocking is a more effective technique
• This belief is maintained even after students see the improvements from using interleaving
• This belief is not removed when students are told that interleaving is better than blocking

How do we deal with this issue?

Like with most things, being consistent is key. One way to do this is by trying to constantly interleave topics across a range of subjects.

Doing this will help expose students to interleaving more, which will help counteract their prior belief that blocking is better.

It is essential to explicitly explain the benefits of interleaving before introducing it and after doing it. Why? One reason is that it helps students link the process to the outcome. However, simply explaining the benefits is found to not be very effective.

In the study, the researchers found that one of the most effective ways to change students’ negative beliefs about interleaving was by:

• Separating the blocking and interleaving study and test sessions;
• Starting with the interleaving session;
• Directly showing students the benefits they are gaining when practising interleaving;
• Using theory-based information to explain why interleaving is better.

Often, teachers wait until it’s close to exam season before introducing interleaving and use it as part of a “study skills” session. By not starting early, students might keep believing that blocking is a more effective technique. Therefore, to ensure that students gain more from this strategy, start using it early.

Final Thoughts

Interleaving is a very useful learning technique and very beneficial in the long term. However, students may have metacognitive illusions causing them to believe that interleaving is not an effective strategy.

To help them overcome this problem, it is useful to be consistent, explicitly explain the benefits to them and introduce this technique early.