The spacing effect and knowledge retention

Examination season is about to kick off and with it comes insurmountable levels of stress, a caffeine addiction and late night cramming. Last minute all-nighters may give the impression of learning but its no more than a temporary knowledge fix. In the long term, the knowledge quickly fades. The impact of the exodus of learning is notably visible in further studies when colleges and universities may expect prior learning. The result may lead to some students to believe that their lectures are being delievered in a foreign language (unless of course it is a language course).

But this scenario is avoidable. You can prepare effectively for assessments and retain knowledge more effectively than traditional cramming or high frequency revision – it is known as the spacing effect.

It’s good to forget

The spacing effect is not new. Ebbinghaus in the late nineteenth century observed its impact as so has countless other researchers in the past century. However, a family of researchers put the spacing effect to the test over days, months and years – not just by minutes or hours.  The Bahrick’s spaced out the revision of foreign language vocabulary over different intervals of time then tested their ability to retain what they had learnt over many years. Their findings suggest that spacing revision at longer intervals can have more impact in retention then study sessions closer together. For instance, 13 practice sessions spaced at 56 days had the same retention rate as 26 sessions of revision every 14 days (Bahrick et al 1993).

What the study suggests is that we can be more effective and smarter with our time if revision is spread out over a period of time. We may not be able to space a set of vocabulary over many years for a test at the end of the term but what the spacing effect demonstrates is that less is more. For instance, Cepeda et al (2008) considers the timeframe in which optium revision impact can be made in preparation for tests within a week, month or year. The key indegredient – spaced intervals.







This in practice feels light years away in schools. The common routine across the curriculum is to cram to deliver all the subject knowledge. Then cram in intervention lessons to cover anything missed in the original cramming session. To lastly prep students to cram days before their examination and pray.

Pretty much cram translates to can’t retain and master. However, science does illuminate possibilities to rethink our planning to include certain strategies that embrace forgetting and helps students transfer short term performance into long term learning.

What can we do?

First is to consider a long term vision to spacing knowledge across whole key stages. Jerome Bruner’s spiral curriculum may provide the structure to deliver an intelligent sequenced body of knowledge. He proposes revisiting key learning each year through the curriculum until the examinations. In each instance the knowledge can be further developed to provide stretch and challenge (see The search for stretch and challenge in lessons) that will help reinforce learning.

Second, whereas the spiral curriculum is spacing key knowledge and increasing the challenge each time, distributed practice is the intentional regularly spaced planning of key knowledge throughout the given year. For example, specialist vocabulary in science is taught or quizzed every month or making reference to a particular event in history when appropriate at different points in the year.

Third, is being more strategic in preparing students to how to revise. This has to be tightly scripted and students trained to execute it. The difficulty lies in that we have to rewire and change student habits of revising (and for parents and students to buy into it!). The urge to study closer to the examination will be the challenge. Discipline is critical to map out a spaced revision timetable that stretches across the year in which students will revisit the topics every month or so. It may be an upfront cost to set up but it will pay dividends in the long run.

Can’t retain and master

It may be hard to digest that to learn we must forget. Cramming will always be the go to method but it can’t help students to retain or master the information. Instead, deliberate spaced intervals that revisit, re-teach or test knowledge can lay the foundation for meaningful long term learning.

Science may not know why the space effect works but its effectiveness is clearly observable. If you have waited to the last minute then cram it of course but the best approach is a long term strategy to retain knowledge beyond the test.



Bahrick HP, Bahrick LE, Bahrick AS, Bahrick PE.(1993). Maintenance of foreign language vocabulary and the spacing effect. Psychological Science, 4, 316–321.

Cepeda, N.J., Vul, E., Rohrer, D., Wixted, J.T., & Pashler, H. (2008). Spacing effects in learning: A temporary ridgeline of optimal retention. Pschological Science, 19, 1095–1102.



Cover image Photo: Crystal Eye Studio/Shutterstock)

Chart image credited to David Didau

Leave a Reply