To Learn, Space Out
Using the Spacing Effect to Boost Retention and Understanding
Procrastination, it seems, is human nature. We tell ourselves there’s always tomorrow. That is, until the day before an exam. Then, typically, there’s a frantic attempt to cram as much information as possible into a single study session. But a one-time encounter with the material, even if it’s a five-hour-long session, is going to do very little to promote long-term learning.
There’s a simple, unintuitive way to study smarter. Simply by breaking up study sessions into smaller, manageable chunks and spreading them out over time, a lot more learning will take place. Researchers who study learning and memory call it the “spacing effect,” and it’s an incredibly powerful and easy way to enhance long-term retention. It has been shown to boost learning in kids as young as two years old, elementary school students, high schoolers, college students, and folks in senior living communities. Across all ages and subjects, studies consistently show that spacing out study sessions over time improves one’s ability to remember and understand information for longer periods.¹
100 Years of Remembering
Learning scientists have known about the spacing effect for a long time. Over 100 years ago, a German researcher named Hermann Ebbinghaus conducted experiments on himself to learn how memory works. In one experiment, he tried to memorize a series of nonsense syllables — like DAX, BOK, and YAT. For some of the syllables, he studied them repeatedly on the same day; for others, he spaced his study sessions apart over several days.
Ebbinghaus discovered that he could retain a lot more information when he spaced out his study sessions — studying a little bit every day — rather than studying a lot of information in one day.²
Hundreds of studies support Ebbingaus’s seminal work. For example, in 2011, thanks to a schedule change at their university, researchers were able to test the spacing effect in their classes. In two different statistics courses, the same amount of material was taught in a two-month class and a six-month class. This meant the students in the first class were forced to cram more studying into a shorter period than students in the second class.
When they received their grades, students in the six-month class outperformed students in the two-month class. Even though they studied the same amount of material for the same amount of time, the students whose study sessions were broken apart over a longer schedule did better. On a final exam that tested their conceptual understanding, students in the six-month class scored much higher than students in the two-month class.³
Why It Works
Learning scientists have several theories on why spreading out study sessions works better than cramming. Some researchers think that when you space sessions too close together, your brain doesn’t have to work very hard to retrieve information from memory. To make matters worse, the ease with which you remember something shortly after studying can fool you into thinking you’ve actually learned it. In other words, trying to learn a subject by cramming is counterproductive, yet it leads to the illusion that it’s working.
Another theory about spaced practice sessions involves reminding. Repeating a study after some time has gone by serves to remind you of what you studied during the first session. By doing this, you retrieve the material from your long-term memory, which enhances your learning (for more on the power of memory retrieval, see Why We Need More Testing, Not Less).
A third theory points to what is called “consolidation.” Each time you study something it builds on the first session, leaving a trace stored in your memory. The second time you study the same material, it benefits from the trace memory you’ve already established. By spacing your study sessions over days, weeks, and months, you consolidate all those trace memories. Thus, unlike cramming, spacing out your study sessions gives your brain the time it needs to stabilize the material in your long-term memory.
Forgetting is the Friend of Remembering
Forgetting is something we typically want to prevent or minimize. But research on the spacing effect shows that forgetting can be beneficial to learning. Consider, for example, an experiment in which students were asked to learn Spanish translations. After an initial study session, students were given six separate review sessions to learn the translations.
In one group, students studied the Spanish words back to back, with no spacing between the six study sessions. As you might expect, such cramming led to almost perfect accuracy after the sixth session.
Another group of students studied the same Spanish words over six sessions, but their sessions were spaced 30 days apart. That’s right, each study session was separated by an entire month. Because the study sessions were spaced so far apart, forgetting was much greater: The students’ initial test scores after the sixth session were much lower compared to the students who crammed.
But here’s where things get interesting. Thirty days after all six sessions were completed, the groups were tested one last time. The students who retained the most information were the ones who spaced their study sessions 30 days apart! Even though it looked like the cramming group was learning more during the study sessions, the spaced group showed better long-term retention.⁴
There are at least two interesting and important implications that can be drawn from this study. First, given that the cramming group did better than the spacing group during the study sessions but then did worse on the final test, initial performance should not be confused with long-term learning (see Learning vs. Performance: A Distinction Every Educator Should Know). Second — and as counterintuitive as it may sound — this work suggests that forgetting can enhance learning. The students in the spacing group forgot more of the translations between study sessions compared to the cramming group, yet it was the spacing group that retained more of the translations on a long-term memory test.
Practical Applications of the Spacing Effect
There are many ways students and teachers can take advantage of the spacing effect to boost retention and understanding. Here are a few:
Build a study schedule and avoid cramming
Break out your calendar and schedule your study sessions by working backward from the dates of your exams. It takes a bit of forethought, but by planning study sessions that are spaced apart (and then actually studying!), more of the information will stick. Cramming, on the other hand, may feel like it’s working in the moment, but it does very little to foster long-term learning. If you are going to cram, make sure that you engage in plenty of spaced studying before you get to that point.
When studying, take a break every half-hour or so. Studying in two 30-minute chunks is better than studying for one hour straight, so set a timer if you need to.
Revisit challenging topics within study sessions
Start a study session off with a difficult topic, then study some other things, and then come back to the challenging topic. Spacing can be achieved within study sessions, not just between them.
Space your curriculum
Reviewing is important, but timing matters. Here’s an example of how you can incorporate three-week-long spacing into your review schedule (I created this example for teaching vocabulary, but the concept is the same no matter what you teach!):
Return to topics after pre-established breaks
It’s common for teachers to move on to a different topic after built-in school breaks, such as recess periods and lunchtime. If possible, revisit pre-break topics after the students come back from these breaks. For example, if you are teaching fractions before lunch, you can have your students do some practice fraction problems right after lunch.
Use Lagged Homework Assignments
Suppose you’re creating a homework assignment relevant to a topic that you covered earlier that day — say, dividing polynomials. In addition to division problems, consider including several problems from previous lessons, such as subtracting and adding polynomials. Sneaking in several problems from lessons that were covered a day, a week, or even a month ago is a great way to integrate spacing into your homework assignments.
Let your students in on the secret
Tell your students about the spacing effect and encourage them to use it on their own. Share this article with them or mention the student applications I mentioned above. When teachers and students are on the same page, real progress can be made.
STUDENTS AND TEACHERS
To get more bang for your buck, combine spacing with other evidence-based learning strategies, especially retrieval practice. For more on these strategies, see Want to Make Learning Stick? Make it Harder.
¹Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T., & Rohrer, D. (2006). Distributed practice in verbal recall tasks: A review and quantitative synthesis. Psychological Bulletin, 132, 354–380.
²Ebbinghaus, H. (1964). Memory: A contribution to experimental psychology (H. A. Ruger, C. E. Bussenius, & E. R. Hilgard, Trans.). New York, NY: Dover Publications. (Original work published 1885)
³Budé, L., Imbos, T., van de Wiel, M. W., & Berger, M. P. (2011). The effect of distributed practice on students’ conceptual understanding of statistics. Higher Education, 62, 69–79.
⁴Bahrick, H. P. (1979). Maintenance of knowledge: Questions about memory we forgot to ask. Journal of Experimental Psychology: General, 108, 296–308.