GUEST POST: Spacing in Teaching Practice

GUEST POST: Spacing in Teaching Practice

By: Jonathan Firth

Jonathan Firth (@psychohut) is a high school teacher of psychology in Scotland with a background in psychology and applied linguistics. He has written some school textbooks on psychology that cover a range of topics, but his main areas of interest/research are long-term memory and metacognition. Jonathan has been working on a few small-scale collaborations and classroom-based research projects, and is now just beginning a PhD in education with a focus on how the spacing and testing effects can be applied to classroom activities/timing and course design.

Like many teachers, I have become intrigued by the idea that simply by changing the gap between two or more learning activities such as explanations or revision, I can help my students do better - the so-called ‘spacing effect’. What wonderful thing is this for the stressed and busy teacher - learning can be much more effective simply by changing the timing? It sounds like a gift to our overworked and stressed profession!

Many of us probably already believe that learning works better when spread over a longer period than with last-minute ‘cramming’. What they might not realize is that this is based on one of the oldest research studies in the history of psychology. In the 1880s, German researcher Hermann Ebbinghaus (1) published a series of findings on memory using the curious method of testing himself on lists of nonsense syllables. Among his findings was the ‘forgetting curve’ - the idea that forgetting happens rapidly at first then slows down. He was also among the first to empirically demonstrate the benefits of spacing. Although his experiments didn’t use classroom-type materials, the same phenomena have since been demonstrated hundreds of times with more realistic tasks.

When you stop to think about it, though, this phenomenon is not actually that obvious - how can a larger gap be beneficial to learning, when it is likely to lead to more forgetting in the short-term? The answer may be that introducing long gaps between study opportunities makes the review/retrieval attempts more difficult - and this difficulty appears to be a critical ingredient in establishing a more lasting memory (2, 3).

For the teacher

Anything that can help a learner use their memory more effectively is of potential interest and use to teachers. Despite its potential, though, spacing is not standard practice in the classroom. Most teachers cover a topic from beginning to end in a matter of days or weeks, and set follow-up homework in the same week. Overall, spacing has been described by Dempster as ‘a case study in the failure to apply the results of psychological research’ (4), and more recent reviews (5) still talk of spacing in terms of its potential.

How then, can we begin to apply spacing in the classroom? One avenue could be to re-design the order of lessons, or of activities within those lessons. A great appeal of introducing more spacing is that it simply involves a change in timing, and not necessarily in materials, techniques or lesson content.  The benefits of spacing can therefore be obtained without any extra work (although it can be very productively combined with other beneficial techniques too, such as active learning or low-stakes quizzes).

Spacing links to another important and beneficial concept: interleaving, i.e., mixing up tasks rather than doing them in blocks of the same type of task. When we introduce a time delay between studying and re-studying, other material will be covered during any class time in-between. This interleaving can have additional benefits, perhaps by helping learners to more clearly see the links and the differences between different topics or sub-topics. In math, for example, interleaving can help learners to choose the correct strategy to solve a problem (6), and the researchers who study these effects therefore advise against giving students exercises that feature several consecutive examples of the same kind of problem.

In other disciplines, could it be advantageous to break up a topic into smaller parts rather than teaching it all consecutively? What about breaking an explanation into parts, or leaving a video incomplete one day and coming back to it a week later? Or setting homework for a given topic two months after it was studied, instead of in the same week? These would seem like promising ideas based on the existing theories or spacing and interleaving - but have yet to be fully tested out in classroom situations.

How does it work?

There could be many reasons why a larger gap between learning and reviewing is more beneficial than a shorter one, or than no gap at all. One is the idea that we simply don’t process repeated information very well - it’s hard to pay attention to it, and the mind wanders (7). Alternatively (or in addition), failing to space out learning might not give us enough time for consolidation - a process that relies on deep sleep - before attempting to build on it.

So, what time delay should I build in to my teaching?

In many courses taught to adolescents, learning typically proceeds in blocks or units. Splitting these into several smaller blocks would be a relatively pain-free tweak for a teacher to make. For example, if 5 topics were taught over a few weeks each, these could instead be interspersed throughout the year.

However, the issue of how to apply spacing in our classrooms is actually far from obvious when you begin to delve into the details. For starters, how much of a time delay is best? Is there such a thing as too much spacing? This question is difficult to study in the classroom because there are so many other variables at play, and it should be noted that the bulk of the research on this topic is lab-based.

Nevertheless, it is likely that many teachers are revisiting topics too soon. In an experimental study of spacing with delays of up to a year, One study recommended leaving a gap before reviewing of around 20-30% of the time between first studying something and the final test/exam (8). If, for example, an exam was 6 months away, this would suggest that conducting a review activity/revision quiz after a month or so would be preferable to doing so within a few days of first studying the material. They also caution that the optimal gap will differ based on many parameters, and while a gap can be longer than optimal, this is preferable compared to a gap that is too short!

My classroom practice and the issue of knowledge level

I have started to try out spacing in my own classroom. In my first classroom study, I took advantage of a naturally occurring break in classes for exam leave, allowing me to measure learning when there was a gap between two lessons compare to two lessons in the same week. Although results were promising, I found it hard to reliably and fully measure outcomes from an entire 1-hour lesson, as so many other factors come into play, leading to ‘noise’ and possible confounds in the data. I therefore moved on to studying performance on a much shorter learning task - something that takes just a few minutes and contains a few specific facts to master. These facts can then be re-studied either immediately, later in the same lesson, or after a delay of a week or more. The initial results I’m finding suggest that the largest spacing is optimal - although I need more time before I can gauge the long-term benefits!

As I have been working on my classroom research, I have also noticed that spacing appears to have a more beneficial effect towards the end of a topic than at the beginning. It could be the case that the optimal amount of spacing interacts with how well developed the learner’s overall knowledge is - if newer to a topic, forgetting will be more rapid, so the delay before a repetition or practice quiz may need to be shorter. I have yet to fully explore this idea, but it is something that I plan to work on over the coming year.

Overall, then, the exact timing may come down to a class’s specific needs and the students’ prior experience. What is clear is that however you do it, spacing (and interleaving) is generally beneficial. Why not try splitting a topic into two blocks, delaying a review session or homework task, or leaving things unfinished at the end of a lesson? I’d love to hear your experiences.

To read more about how other teachers use interleaving in the classroom, check out our Weekly Digest on this topic.


(1) Ebbinghaus, H. E. (1964). Memory: A contribution to experimental psychology. New York, NY: Dover. (Original work published 1885)

(2) Bjork, R. A. (1994). Memory and metamemory considerations in the training of human beings. In J. Metcalfe and A. Shimamura, (Eds.), Metacognition: Knowing about Knowing (pp. 185–205). Cambridge, MA: MIT Press.

(3) Roediger, H. L., & Karpicke, J. D. (2011). Intricacies of spaced retrieval: A resolution. In: A. S. Benjamin (Ed.) Successful Remembering and Successful Forgetting: Essays in Honor of Robert A. Bjork (pp. 23-47). New York: Psychology Press.

 (4) Dempster, F. N. (1988). The spacing effect: A case study in the failure to apply the results of psychological research. American Psychologist, 43(8), 627-634.

(5) Kang, S. H. (2016). Spaced repetition promotes efficient and effective learning policy implications for instruction. Policy Insights from the Behavioral and Brain Sciences, 3(1), 12-19. doi: 10.1177/2372732215624708.

(6) Rohrer, D., Dedrick, R. F., & Stershic, S. (2015). Interleaved practice improves mathematics learning. Journal of Educational Psychology, 107, 900-908. doi: 10.1037/edu0000001

(7) Phillips, N. E., Mills, C., D'Mello, S., & Risko, E. F. (2016). On the influence of re-reading on mind wandering. The Quarterly Journal of Experimental Psychology, 1-20.

(8) Cepeda, N. J., Vul, E., Rohrer, D., Wixted, J. T., & Pashler, H. (2008). Spacing effects in learning a temporal ridgeline of optimal retention. Psychological Science, 19(11), 1095-1102.