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Interleaving learning strategies and knowledge retention

Mixing it up

Learning design can be a complex process which should always begin by asking the question ‘Why?’, before moving on to the ‘What?’ and the ‘How?’ With so many variables in the mix, we already know that one learning design approach does not fit all: spacing, spirals or interleaving learning strategies for knowledge retention, where do we go next?

Interleaving learning strategies

Spacing, spirals and interleaving

A key skill in learning design is the ability to articulate the rationale for taking a particular approach. Terminology is everything! To communicate clearly, we need to understand the terminology we are using and how it impacts our design.

We see so many articles advocating the benefits of spacing, spirals and interleaving but what do they really mean? Let’s take a look …

Massed practice

In massed practice, we cover separate topics as blocks. As the learner, if we don’t practice retrieving this knowledge over time, it is easy to forget what was covered in earlier topics.

Spaced practice 

We use spacing to extend a learning experience over a period of time. Instead of designing an experience as a block of 1-day duration, we could chunk this down and spread it out over a 6-week period in sessions of 1-hour per week. This approach allows time for reflection in-between with each session designed to stimulate recall of the content covered in the previous session. This spacing and retrieval over an extended period improves recall of the topic, in comparison to massed practice.

spaced practice

Spiral learning

When we talk about spirals in learning design we are often referring to the concept of a ‘spiral curriculum’ (Bruner, 1960). In spiral learning, content for a topic is initially covered at a simple level. Opportunities are provided to apply this new knowledge with revision activities to consolidate learning. A spiral curriculum will revisit the same topic multiple times—each time increasing the depth of exploration and adding more detail—with application activities becoming more complex. The goal here is to work towards mastery of a topic by learning the basics and then building upon this by returning and going deeper each time. 


We can think of interleaving as the opposite of massed practice. Instead of practising and completely mastering one topic before moving on to the next, with interleaving, we practice a topic for a shorter period of time before introducing other topics to the mix. For example, if we had 3 topics to cover, we could start by practising Topic 1, move on to Topic 3, then Topic 2 before returning to practice on Topic 1 again. The introduction of other topics is not a sequential process and can appear to be random.

interleaving learning strategy

Is interleaving the answer to improving knowledge retention? 

Well, that depends on your perspective … 

In ‘Make It Stick: The Science of Successful Learning’, (Brown, Roediger III and McDaniel, 2014) a number of case studies are used to illustrate the benefits of interleaving. 

In the case of learning mathematics, a typical textbook or massed practice approach would be to cover one topic at a time, mastering each topic before moving on to the next one. Now, what happens when the learner sits an exam and has to recall this knowledge? Exam questions are generally presented in a random order which makes recall more difficult as learners have become familiar with the blocked approach where the strategy used to solve the problem is repeated. (Rohrer and Taylor, 2007). 

Where interleaving demonstrates benefit is in helping the learner to develop ‘discriminatory skills’ (Brown, Roediger III and McDaniel, 2014). Due to the way that topics are shuffled and practised randomly, the learner needs to identify what the example or problem is before selecting and applying the correct strategy to tackle it. This develops higher-order skills of being able to compare and contrast a wide range of scenarios in addition to identifying appropriate solutions. 

The development of discriminatory skills is highlighted in another study where painting styles of a number of artists were presented to learners using two approaches—massed practice and interleaving (Kang and Pashler, 2012). The interesting result of this study was that although learners performed better after following the interleaving approach, many reported that they felt that the massed approach was the most effective learning strategy for them. This opinion persisted even after discovering their results.

Learning isn’t an easy process and interleaving lacks the instant gratification and feeling of accomplishment that can be gained by massed practice ‘cramming’. The case studies detailed here and beyond in the book ‘Make It Stick’ acknowledge the additional challenge of interleaving but also report improved outcomes in the longer term.

knowledge retention

Summary: how mixed practice can boost your learning design

Let’s consider the design approach for online courses which are often self-directed without facilitation. As a learning designer, it is important to ensure that we introduce appropriate support and scaffolding to avoid frustrating and overwhelming the learner with ‘extraneous cognitive load’ which is caused by the difficulty involved in the task of learning itself (Sweller et al, 2011).

A way of providing scaffolding, to support the learning process, is to use worked examples—step-by-step instructions of how to solve a problem.  We can start by using worked examples that provide ‘high task support’, which we gradually reduce to ‘low task support’ (Neelen and Kirschner, 2020). The phased reduction from a high level of detail and instructional support to a low level of detail within the worked examples gently removes the scaffolding as the learner progresses.

To provide automated feedback, we can introduce formative assessment activities, such as quizzes. The use of quizzes enables learners to practice retrieval of information while receiving immediate feedback to keep them on the right path and celebrate their success along the way. 

If cohorts of learners are going through a program together, we can design discussion threads for peer support and provide structured prompts to initiate valuable conversations.

An essential element to include in interleaved learning design is activities in multiple formats where the rules and strategies required to be applied don’t relate to only one topic. This introduces variety into the learning experience. The randomness of variety enables the learner to draw upon those higher-order skills of compare and contrast by matching the appropriate strategy to the activity.

Of course, in addition to spacing of all types, there is the impact that emotion has on learning. Using storytelling techniques can bring a topic to life and appeal to our ‘affective context’ (Shackleton-Jones, 2018). If we care about something and can see how it relates to our own context, we store our emotional response—how we feel—in our memory. 

How learners feel about their learning experience is important too. As we saw in the results of the previously mentioned Kang and Pashler study, interleaving can make the experience feel more difficult.  Interleaving has its place and, although proven to enhance the ability to answer more complex questions, it won’t necessarily be the best solution to every problem. The learning design of a course should not make the process any more difficult for the learner than is necessary.

In summary, as learning designers we need to ask the big questions up front: ‘Why are we creating this learning experience? What problem are we trying to solve? How will we measure success? and ‘Who are we designing for?’ Only when we understand the real need and put the learner firmly at the heart of the learning experience can we then select the most efficient and effective approach to achieve our goal. 

mixed practice


Brown, P., Roediger III, H. and McDaniel, M., 2014. Make it stick: the science of successful learning. Dreamscape Media.

Bruner, J. 1960. The process of education. Harvard University Press.

Kang S. H. K. and Pashler A. 2012. Learning painting styles: Spacing is advantageous when it promotes discriminative contrast Applied Cognitive Psychology Published online 2 May 2011 in Wiley Online Library ( DOI: 10.1002/acp.1801 Available at: [accessed 15th August 2021]

Kornell N. and Bjork R. A. 2008. Learning concepts and categories: Is spacing the “enemy of induction”? Psychological Science.

Neelen M. and Kirschner P. 2020. Evidence-Informed Learning Design: Creating Training to Improve Performance. Kogan Page.

Rohrer D. and Taylor K. 2007. The shuffling of mathematics problems improves learning, Instructional Science.

Shackleton-Jones, N., 2019. How People Learn: Designing Education and Training that Works to Improve Performance. Kogan Page.

Sweller, J., Ayres, P., & Kalyuga, S. (2011). Cognitive load theory. Springer.