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  • Rebecca Savill

Spacing and Interleaving

In this short series of blog posts, we'll explain the research around some of the most established theories in learning science.

What it is

Spacing is a learning technique which has been extensively studied for over a hundred years(1).

It is just as it sounds: spacing out your study sessions rather than cramming all of them into one period.

Interleaving is the practice of switching between different topics for each of your study sessions. It is the natural companion to Spacing, allowing you to practise Spacing in an efficient way. If you only used Spacing to study it would take you a long time to learn a single topic and you’d spend the majority of that time twiddling your thumbs. However, by incorporating Interleaving you can study multiple topics concurrently, maximising your learning time.

Why it is beneficial

Spacing has been shown to have a dramatic effect on the ability to retain information(2). It has one of the strongest effects in memory science and is extremely easy to incorporate into your studying schedule.

Everyone is guilty of leaving their study until the night before the exam or writing their big paper only a few days before it’s due. However, we also know intuitively that cramming information isn’t very effective long term. Research backs this up(3) again(4) and again(5) across a wide range of academic(6) and physical(7) learning situations. Cramming may help you pass an exam but you’re very unlikely to retain any of that knowledge for the long term.

The best thing about using Spacing and Interleaving is that it actually saves you time; you can study much more efficiently and in less time than by cramming a topic.

How does it work

One of the leading theories of memory science comes from Bjork and Bjork (1992)(8) and posits that your ability to retain information is determined by your brain’s Storage Strength and Retrieval Strength associated with that information. Storage Strength is concerned with your long-term ability to retain information and Retrieval Strength is concerned with your ability to recall that information when you need it.

It may sound counterintuitive, but according to their findings, Spacing works because it gives your brain a chance to forget some of the information you’ve studied before refreshing your memory again. These periods of forgetting and refreshing improve Storage Strength for that information.

The process of refreshing your memory on a topic also helps you to create new cues for retrieval of that information(9). For example, if you had previously watched a video on a topic and then later discussed the topic with friends, you would now have two cues for recalling that same information; the video and the conversation.

Interleaving helps speed up the forgetting process as switching your focus from one topic to another makes it harder to remember the previous topic you studied. Retention Strength is also helped as it allows you to make connections between the different topics you are studying(10).

So how long should you leave it between study sessions? Well, one study conducted by a group of researchers in 2008(11) shows a rough correlation between the length of the spacing and how long the information is retained. In essence the longer the spaces between study sessions, the longer you will retain the information. They produced a reference chart to aid with spacing which is reproduced below:

Time to test

First study interval

1 week

1-2 days

1 month

1 week

3 months

2 weeks

6 months

3 weeks

1 year

1 month

As a general rule, if you try to restudy information and are finding it easy or can remember the details of the topic without much difficulty then your study sessions are too close together and this is actually more similar to cramming.

Are there limitations?

Spacing and Interleaving can have benefits for short-term goals such as passing an exam in a couple of weeks but the impacts are far greater with long-term learning such as throughout a degree-level course for building expertise throughout your career.

If you need to pass a test within a very short timeframe then it’s best to cram for that test. Afterwards, however, it would be best to restudy that information using Spacing and Interleaving in order to retain it for the long-term.

Find out more

This is just a quick overview about Spacing and Interleaving to get you started and using the technique. More information can be found in the following places:


  • How we learn: Throw out the rule book and unlock your brain’s potential by Benedict Carey.

  • Grasp: The Science Transforming How We Learn by Sanjy Sarma



  1. Ebbinghaus, H. (1913). Memory: A contribution to experimental psychology. (H. A. Ruger & C. E. Bussenius, Trans.). Teachers College Press.

  2. E. L. Bjork and R. A. Bjork, "Making Things Hard on Yourself, but in a Good Way: Creating Desirable Difficulties to Enhance Learning," in Gernsbacher, Psychology and the Real World, 56-64.

  3. Jonathan A. Susser and Jennifer McCabe "From the Lab to the Dorm Room: Metacognitive Awareness and Use of Spaced Study," Instructional Science 41, no. 2 (2013): 345-63.

  4. Nicholas J. Cepeda, Noriko Coburn, Doug Rohrer, John T. Wixted, Michael C. Mozer, and Harold Pashler, "Optimizing Distributed Practice: Theoretical Analysis and Practical Implications," Experimental Psychology 56, no. 4 (2009): 236.

  5. Doug Rohrer and Kelli Taylor, "The Effects of Overlearning and Distributed Practise on the Retention of Mathemat ics Knowledge," Applied Cognitive Psychology 20, no. 9 (2006): 1209-24.

  6. Haley A. Vlach and Catherine M. Sandhofer, "Distributing Learning over Time: The Spacing Effect in Children's Acquisition and Generalization of Science Con cepts," Child Development 83, no. 4 (2012): 1137-44.

  7. Carol-Anne E. Moulton, Adam Dubrowski Helen MacRae, Brent Graham, Ethan Grober, and Richard Rear "Teaching Surgical Skills: What Kind of Practice Makes Perfect A Randomized, Controlled Trial," Annals of Surgery 244, no. 3 (2006) 400.

  8. Bjork, R. A., & Bjork, E. L. (1992). A new theory of disuse and an old theory of stimulus fluctuation. In A. F. Healy, S. M. Kosslyn, & R. M. Shiffrin (Eds.), Essays in honor of William K. Estes, Vol. 1. From learning theory to connectionist theory; Vol. 2. From learning processes to cognitive processes (pp. 35–67). Lawrence Erlbaum Associates, Inc.

  9. Lynn L. Siegel and Michael J. Kahana (2014). A Retrieved Context Account of Spacing and Repetition Effects in Free Recall. Journal of Experimental Psychology: Learning, Memory, and Cognition 2014, Vol. 40, No. 3, 755–764

  10. E. L. Bjork and R. A. Bjork, "Making Things Hard on Yourself, but in a Good Way: Creating Desirable Difficulties to Enhance Learning," in Gernsbacher, Psychology and the Real World, 56-64

  11. N. J. Cepeda, E. Vul, D. Rohrer, J. T. Wixted, and H. Pashler, "Spacing effects in learning: A temporal ridgeline of optimal retention," Psychological Science, 19, 2008, 1095-1102.


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