Spaced Repetition vs. Massed Practice: The Honest Comparison
The research on spaced repetition is overwhelming and the implementation in most classrooms is minimal. A practical guide to what the studies actually show and how to use spacing without committing to a study...
There is considerable cognitive science research regarding the effectiveness of spaced repetition for distributed practice of material to be learned. Indeed, the finding that distributed practice (e.g., studying a topic for 60 minutes on a single day) results in long-term retention that is greater than that resulting from massed practice (e.g., studying the same topic for 60 minutes on three different days, with 2 days of no study in between) of equivalent total duration has been replicated so extensively that it is considered to be a robust finding. However, the findings of such research have not had a great deal of impact on how most people study, whether in classrooms or out of school. This article reviews some of the evidence, and then examines some of the reasons why the findings have not resulted in more practice of the type found to be effective. This article will also present some practical advice, derived from prior research, on how to put the findings into practice. The findings will be reviewed in a 2025 report from the Cognitive Science Society.
What the Research Shows
First, there is the finding itself. If a student studies 60 minutes straight a day or two before for a long period of time to really solidify information in their long term memory and compare that to the same amount of time distributed in three 20 minute studying sessions a few days apart, the student will retain information significantly longer if they studied in the distributed manner of the 20 minute sessions, three in total over the course of a few days. This effect is also referred to as the spacing effect. Studies show that all sorts of content can be studied in distributed ways over a period of time to retain more in the long run. A meta-analysis showed the effect-size for spacing was on average 15-30% for final retention after massed practice of equal duration in all of the many studies. Skip that.
Why Classrooms Default to Massed Practice
Most unit plans are set up in massed practice format: e.g. a week on the French Revolution, a week on cell biology, a week on quadratic functions. This is convenient for teachers and students alike. It is easy to set up and to schedule into a school calendar. Students and teachers alike are used to such units, and so are accustomed to ‘studying’ in a short space of time for a test that follows the unit a few weeks later. The fact that the material is learned in a short space of time (massed practice) leads to high scores in the first test after the unit. The costs are often invisible, and therefore forgotten.
“Your system is set up to optimize for the test at the end of the week. You’re not really set up to handle the test three months later where it’s just going to show up in another subject and you’ve already forgotten it all,” says Vasileios Karadimas of his work on study strategies for classroom learning at the University of Edinburgh.
What Spaced Implementation Looks Like
In terms of the structure of the study of material, rather than trying to implement a load of review just before a test, teachers who do use spaced repetition usually do so by having a few brief retrieval sessions on different days. For example, a 5 min warm up of questions on the earlier material in a lesson could be enough to induce the spacing effect, and need add only a little to the normal running of the class. I did this in my last attempt at using spaced repetition for study, and it worked well for me.
Other approaches to spaced review are to distribute review of past material that students did well on throughout the time that they are studying other material that they are currently studying. In other words, rather than making students do review of past material all at one time, teachers could have students review 2-3 problems from a month or so ago in each of their homeworks, and from 2 weeks ago in every other homework, and from 1 week ago in every third homework. This would have the effect of keeping all of the material that students learned well before now actively in rotation.
The Resistance Pattern
It is common for students to resist distributed learning because of their negative reactions to having to study something that they had previously learned. What they do not know is that just having covered material previously does not mean that they have mastered it. In fact, there is plenty of evidence to show that students remember more after a period of distributed review than after a period of massed review of equal length. This is because the material is retrieved after some forgetting has occurred and so, each time, it is retrieved more slowly and with more effort than before. But it is just this slower and more effortful retrieval that strengthens the memory of the material.
“Even if they hate it at first,” continued the high school teacher, “students love the feeling of being in control and mastering material. That they prefer to study in the way that they used to because they could remember everything during the test-week is not the goal of spaced review. The goal is to have students remember things in April that they studied in September. That is so much harder than remembering things for a test that takes place in the week of the test.”
Apps and Tools
Several apps automate spaced practice for self-directed learners. Anki, Quizlet, and Brainscape all implement variations of the algorithm. The tools work well for fact-based content (vocabulary, dates, formulas, definitions) and less well for higher-order skills that depend on integration and application.
In addition to keeping a small notebook with all of these thoughts have been scribbled in there over the past few years. Half of this article was even written in there.
What Students Can Do
Students can adopt the practice of distributed learning for their own academic purposes. All one has to do is to review, for example, new information the day after it has been learned, two days after, a week after, and two weeks after. The time required for such distributed review is very little and the gains in retention are large.
Another obstacle for the use of spaced repetition is students’ perception of it. Students may feel that they are not learning enough when they review material in spurts rather than in a solid block of time. The sense of not mastering a subject for a time is uncomfortable and can give the impression that the student is failing in some way. This sense of temporary inadequacy can be enough to deter a student from implementing a practice that they have come to believe is effective from reading about it.
The Implication for Curriculum Design
But of course, there is more to pedagogical change in education than just the accumulation of evidence for change, and the root cause of the persistence of massed practice of the kind that is typical of unit plan organization of the curriculum is that there are strong structural and incentives that are at work in a system designed for the test that comes at the end of a unit. That is, the system is already ‘optimized’ for that test, and the evidence for spaced practice of the kind that is described in the research on the spacing effect is not yet sufficient to counter the many structural and other incentives that would have to be overcome in order to bring about a change in that status quo. The work of creating the kinds of structures that would support a very different kind of school is not easy, and schools in which such work is done are likely to be very different from other schools.
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