‘Spacing’ refers to revision throughout the course of study, while ‘interleaving’ means switching between ideas while you learn. Both techniques can help boost students’ long-term memories and retrieval of key information. Helen Webb explains

Having embedded a variety of retrieval strategies into my own practice (SecEd, 2017) I have focused this academic year on introducing interleaving and spacing as effective learning strategies to students.

In this article, I will give an overview of some of the research, and how this has had an impact on my own practice and in our science department to improve student learning.

For a more in depth review of the research I recommend the excellent book – Understanding How We Learn (Weinstein, Sumeracki & Caviglioli, 2018) – where much of the inspiration for this project came from.

The two approaches

The two concepts are similar but essentially spacing is revision throughout the course, whereas interleaving is switching between ideas while you study. Although interleaving and spacing are different interventions, the two are linked because interleaving inherently introduces spacing.

Although cramming the night before a test can yield some positive results in the short-term, the material is more easily forgotten. Spacing (also known as distributed practice) boosts both retrieval and storage strength and is a far better revision strategy for terminal exams.

Many of us will be used to teaching one concept at a time – known as blocking. Most textbooks are also organised in this way. A chapter on one idea is usually followed by a series of questions on that idea. However, there is some research (mainly focusing on sports coaching or maths teaching) in support of interleaved teaching (Hall et al, 1994).

According to Rohrer (2012), interleaving can help you see the links, similarities and differences between ideas more easily. When students encounter a set of concepts (terms or principles) that are similar in some way, they might mistake one word for another word with a similar spelling (e.g. mitosis v meiosis). It is reported that these kinds of errors occur more frequently when all exposures to one of the concepts are grouped together. For example, when all the questions in an assignment or a lesson are devoted to one concept.

Some evidence has shown that if you interleave different concepts together, e.g. follow a question on one concept by a question on another concept, this can produce better test scores. However, at this stage the evidence is still fairly limited.

There are a number of studies that repeatedly find that interleaving in maths lessons (although more challenging in the early stages) improves overall final test scores. This is because solving a mathematics problem requires students to not only know which strategy is appropriate but also how to execute the strategy. For example, one lesson’s tasks are devoted to adding fractions and another lesson on multiplying fractions – both are superficially similar tasks but are ones that require differing strategies.

With blocked practice, students do not need to identify an appropriate strategy because every problem in the assignment can be solved in the same way. At the end of the lesson, simply asking students to complete a variety of questions that involve having to select the right strategy as well as executing it solves this issue.

In practice

It is worth noting that students may be resistant to interleaving because it increases the difficulty of a question or problem. Also, the benefit of blocking content into one lesson allows for scaffolding, which increases the perception of “easiness” and is also perhaps a better way to teach new concepts.

When interleaving, students will probably make more mistakes initially and work more slowly. Students might also have to refer to earlier chapters of their textbook for support. I found that providing students with page numbers for the relevant information and also warning them of the increased difficulty helped.

In practice teachers and students may choose to rely on a combination of blocking and interleaving strategies. There are only limited number of studies that look at the combination of blocking and interleaving, which may well be the optimal approach.

Certainly for subjects like science, the research does not appear robust enough to justify rearranging the whole curriculum or schemes of work at this stage. It is probably better for teachers to focus more on spaced practice than interleaving – but keeping in mind that during each individual study session, it can be helpful to mix up studying different ideas or answering different types of problem.

With this research in mind, here are some simple ways (tried and tested by me) to introduce and model spacing and interleaving as a study strategy into your lessons.


A quick one-to-five quiz in the first five minutes of the lesson (e.g. three questions from the last lesson, one question from last week, and one question from last year).

Multiple-choice or short-answer quizzes staggered throughout the course. These could be on paper, online (for some ideas, see SecEd, February 2018), in-class or for planned, lagged homeworks.

Remind your students that pressurising your memory to recall previously covered information helps to embed it into your long-term memory. However, this testing needs to be low-stakes; there should not be negative consequences for not doing well.

Flash cards

Students can use their revision guides to write their own revision flash cards, where they write key words or questions about concepts on the front and the definition or explanation on the back.

After self-testing, encourage students to sort the flash cards into two piles – information students recalled correctly and ones that they did not. Repeat the self-testing and checking process focusing only on the cards that students recalled incorrectly until there are no cards left in that pile.

To illustrate how students can space out their learning and interleave topics when studying, ask students to keep their flash cards with them and provide opportunities for students to test themselves using all their flash cards in subsequent lessons to improve long-term retention and learning. Once they have done this, ask students to lay out their flash cards with the key terms facing up and ask them to make connections between the words and concepts and then with the new lesson objectives or new topic that you are studying (you can also challenge students to think of real-life examples of each of the concepts too).

Comparing and learning model answers

Following a GCSE biology mock exam, I had success with the following DIRT (dedicated improvement and reflection time) strategy, which enabled me to successfully model both interleaving and spacing strategies to students.

I challenged students to learn two completely different tricky six-mark model answers by rote by the end of the lesson (strategies about how they did this were given).

During the lesson I circulated and listened to students recall the information as and when they were ready. By the end of the lesson, the majority of a very mixed ability class could recite at least one of the two top-level answers by heart. This was a really good opportunity to provide students with very specific and immediate verbal feedback or to question, check and further improve their learning and understanding.

At the end of the lesson I asked students to look again at both model answers and to identify which topics the different strands of the questions related to. This was to reiterate that all topics needed to be revisited when revising for terminal exams.

I then asked students to make links between the two very different questions. This was a lovely demonstration of interleaving in practice and showed how the different topics they had studied connected. It also indicated to me the depth of their understanding.

In their next lesson, I re-introduced the idea of spacing. I explained that recalling something immediately after you have learnt it is relatively easy. Now that they had had some forgetting time, I asked them to again recall everything that they had learnt previously.

In doing so, I was able to highlight the importance of repeatedly revisiting previous learning to prevent forgetting and improve learning.

Cumulative testing

In order to improve students’ study skills and gain some consistency across the faculty, one solution we have trialled has been to introduce cumulative testing across key stage 3 science. At the end of each science topic, students now complete a 40-minute ramped test.

Approximately half of the questions directly assess the topic that students have just completed, and half assess previous knowledge from earlier topics. Where possible I have tried to select past exam questions that relate to the current topic in some way.

This strategy encourages students to revisit earlier topics when revising. Students gradually increase the breadth of what they need to study throughout the course, rather than completing a series of small discrete tests followed by one overwhelming end of year or key stage exam, with content they have not revisited since the original lessons.

In terms of consistency of teaching, it also encourages all teachers in the faculty to revisit earlier topics in lessons or for homework. It also makes feedback following a test more purposeful as students and teachers know that material will be revisited.

Revision lessons

In preparation for exams, students are given a series of revision lessons that explain the research and rationale behind a variety of effective study strategies (e.g. retrieval practice, spacing, interleaving, concrete examples, etc). Each revision lesson then modelled that strategy using the content they were revising for the exams.

  • Helen Webb is an experienced science and biology teacher and lead practitioner with a professional interest in developing CPD for teachers. Her CPD packages are available on Tes. Helen works at Lutterworth College in Leicestershire. Visithttps://helenfwebb.wordpress.com or follow her @helenfwebb. Read Helen’s previous SecEd articles at http://bit.ly/2cLa6UZ

Further information & research

  • Revision and study skills: Retrieval practice, Helen Webb, SecEd, October 2017: http://bit.ly/2TEBpFM
  • Understanding How We Learn: A visual guide, Weinstein, Sumeracki & Caviglioli, Routledge, August 2018.
  • Contextual interference effects with skill baseball players, Hall, Domingues & Cavazos, Perceptual and Motor Skills, July 1994: http://bit.ly/2T7CXmq
  • Interleaving helps students distinguish among similar concepts, Rohrer, Educational Psychology Review 24, 2012: http://bit.ly/2YkZEHK
  • Study skills: Using online quizzes, Helen Webb, SecEd, February 2018: http://bit.ly/2EVKLm4