Of all the buzzwords flying around the world of education at the moment, I think the one that is causing the most confusion is “interleaving”.

What is interleaving? The principle is that rather than teaching a single topic in one block, teachers teach several topics at the same time. Pupils have to switch their attention between two or more topics, and while this may impair their performance in the short term, it should lead to better retention in the long term.

This, according to Elizabeth and Robert Bjork (2011), makes interleaving a “desirable difficulty”.

Sean Kang (2016) suggests that teaching topics in this way will aid retention in the long term, helping pupils to transfer what they have learnt to new situations. One reason for this benefit, suggest Yana Weinstein and Megan Sumeracki in their book Understanding How We Learn (2018), is that interleaving more closely mirrors real life. Life isn’t presented in neat blocks; in the real world, we don’t know exactly what information we will need to use ahead of time, but have to choose the solution from all the information available to us in the moment.

Quick read: How ‘spaced practice’ boosts pupil recall

Quick listen: Robert and Elizabeth Bjork on memory

Want to know more? 5 things every teacher needs to know about research

So, there is plenty of evidence to support the use of interleaving. But how do we use the technique in the classroom?

Applying interleaving

A 2005 study by Lindsey Engle Richland et al demonstrated that when material about astronomy is taught using interleaving, pupils are better able to answer more complex questions than when the material is presented in a logical "block". There are countless opportunities to similarly interleave topics across subjects in school.

Art teachers might teach pupils to recognise the style of different artists by showing them a range of works at one time, rather than studying each artist in turn. Geography teachers might explore how people respond to disasters by interleaving a range of case studies rather than teaching these one after another.

This might sound simple, but there is still much we don’t know about interleaving.

For instance, according to a study by Hannah Hausman and Nate Kornell (2014), interleaving is only effective if the material being interleaved is related. The study showed that interleaving Indonesian vocabulary with anatomy terms, for example, will have no benefit, but suggested that the technique should instead be used to help pupils to compare and distinguish between different pieces of related material.

However, nobody knows exactly how similar material needs to be to make interleaving truly effective.

We also don’t know what impact switching between topics will have on pupils’ initial learning, although the benefits for long-term retention seem clear.

At what point might this difficulty become undesirable? Weinstein and Sumeracki point out that, away from the laboratory, it is very difficult to differentiate between the benefits accrued from interleaving and those from the spacing effect.

Interleaving is not about curriculum design

In fact, when we look at what many teachers are calling “interleaving”, what we often see is a form of spaced practice where material is introduced at one point and then returned to later, taking advantage of the testing effect (see "Why an interleaving curriculum could improve retention"). Pupils are rarely taught something in one block of massed practice and then left to never return to it again. Instead, instruction and practice is spaced out with pupils returning to the topic at regular intervals.

While this form of spacing in the curriculum may work wonders at the end of an English GCSE where the teacher sees their pupils most days, it is less likely to work in most subjects where lessons are more spread out. I recently met with a head of department who had been to a training session that included advice on creating an “interleaved” curriculum. It was suggested that rather than teaching their next unit of tectonics in a block, they broke it up: teaching a lesson on tectonics, the next on rivers, and then one on urbanisation before returning to tectonics.

Not only is this not interleaving, it is unlikely to be effective spacing. The class will have too long a break between their first and second lessons on tectonics, and the approach will just lead to confusion for everyone involved and a very fragmented curriculum.

‘Interweave’, don’t interleave

So what can teachers do? I would suggest that there is a more effective way to approach interleaving, spacing and retrieval in the curriculum. I would call this approach interweaving. In this approach, we identify themes and concepts that recur throughout different topics and plan to teach them in the context of those topics.

For example, in our Year 8 curriculum we consider the role of tectonics as a force that shapes our planet. We could teach this in one block, but instead we weave tectonics like a thread throughout a number of topics.

In the first topic, pupils consider the mechanism behind plate movement and the formation and impact of volcanoes. In the next topic, they look at East Africa, and as part of this, the tectonics thread re-emerges when they look at how the Great Rift Valley formed and how it affects people today. The next topic considers our local landscape and the role of tectonics in the creation of anticlines; and the final topic looks at Haiti with the thread continuing, as pupils learn how earthquakes are caused and about the impact of tectonic hazards on the country’s development. This allows pupils to re-encounter the material in a more meaningful way.

In this approach, we can look for times when genuine interleaving might be appropriate. For example, when we want pupils to contrast the impact of different volcanic eruptions and so teach these at the same time, rather than sequentially.

However, what we are not doing is trying to make interleaving a curriculum planning tool. It is the wrong tool for that job.

Interleaving is a fascinating idea but, as with so many other good ideas, we run the risk of it becoming distorted and misunderstood in the desire to apply it to the wider curriculum or to apply it in the same way to different subjects.

So rather than interleaving, let’s think about how we can better weave the tapestry of our curriculum to build the bigger picture of our subject.

Mark Enser is head of geography and research lead at Heathfield Community College. His book, Making Every Geography Lesson Count, is out now

Further reading

• Bjork Learning and Forgetting Lab
• The Learning Scientists
• Professor Dylan Wiliam on memory