Spaced Repetition

spaced repetition title

The most successful students are not simply those who put in the most time studying. Putting in the time is important, of course, but it’s also critical to use effective strategies. Highly successful students employ a variety of methods to enhance their learning and gain more from the time they dedicate to school. Today, I’d like to focus on just one of these strategies: spaced repetition.

Spaced repetition is a technique that has been proven to form stronger memories in less total time than most other study methods.1 Spaced repetition has also been shown to improve skills more quickly than traditional practice regimes.1 Furthermore, spaced repetition helps students achieve deeper understandings of complex content.1 It even enhances creativity.1 In other words, spaced repetition is one of the foundational skills of academic success.

Users of this technique approach new academic content in a very particular way. They make sure to reengage with the material soon after it is first presented. Many users of spaced repetition strive for three additional exposures to new information within the first 24 hours of learning it. Following that, they aim to revisit the content daily for the next week. After the first week, they make a point of revisiting the content from time to time so it doesn’t fade from memory.

While this may sound like a great deal of work, it’s important to note that none of these exposures needs to be very lengthy. In fact, most users of spaced repetition study for shorter spans of time than students who don’t use the technique; they just study more often. Both users and non-users might put in the same total time over the course of a week, but the users of spaced repetition get more out of their time. They understand the material better, recall it more readily on the test, and remember it more clearly years down the road.

Skills, such as long division or factoring quadratics, are learned more deeply when students practice a little bit each day, as compared with students who practice for a long period of time just once a week. It is almost certainly better to do two long division problems each day than to do 20 long division problems on Tuesday, even though the latter includes six more problems than the former. Here at Northwest Educational Services, we advocate for a “small dose, high frequency” approach to studying. Consistency is more important than intensity.

Some students even apply spaced repetition within a single homework assignment. For example, if a student has a long math assignment with three types of problems, there is a ripe opportunity to use this technique to get more value from the homework. The clever student would do half of the problems in each section, and then cycle back through and do the second half of each section. By the time she’s completed the entire assignment, she’s gotten in two rounds of practice with each of the three skills rather than only one: same number of problems, twice the learning.

There are several reasons why spaced repetition is so effective. First of all, it taps into how the brain naturally forms memories. Basically, the brain is an efficiency machine that tries to avoid using resources to form memories, which means that the brain has to be convinced to remember things. One way to convince the brain to form a memory is to have the information be significant.2 If it feels important, we’ll naturally remember it. The significance of the information allows the brain to justify using resources to remember it.

Making the Boring Seem Important

The second way we naturally form memories is through repetition.2 This is actually significance in disguise: If something appears in our environment over and over again, the brain starts to see it as important. Essentially, the brain decides that, because we keep encountering this information, it must be worth remembering. Because many students find much of their school’s curriculum boring, spaced repetition is a critical strategy. It tricks the brain into thinking that boring information is really important.

Seeing something repeatedly for three hours straight, however, doesn’t have this effect. The brain requires gaps between exposures to the information in order to be convinced to remember it. Because of this feature of the human brain, studying should be broken up into smaller chunks, and students should alternate between subjects during extended study sessions. This applies to all forms of studying, but it has especially important implications for last-minute cramming.

Let’s imagine a student who has waited until the final day to study for two exams – history and biology – both of which are on Monday. The student knows that he needs to spend about six hours of Sunday studying to be adequately prepared for the exams. Rather than devoting three hours to history and then three hours to biology, he would be much better off spending one hour on each and cycling through both subjects three times. This process would effectively cram three spaced repetitions of each subject into a single day, greatly improving how much he would remember.

Laying Brick

Learning expert Dr. Barbara Oakley gives us another reason why spaced repetition is so effective. Building on the idea that learning is a process of growing new connections between neurons, she points out in both her book, A Mind for Numbers, as well as in her Coursera class, “Learning How to Learn,” that neural connections take time to grow, and that the gaps between study sessions provide time for this growth.1

Neural connections:

neuroplasticity neuron

Dr. Oakley uses the metaphor of laying brick to explain. If you want to build a tall, brick wall, she says, you cannot build it in a single day because you have to allow time for the mortar between layers to dry. If you try to add new layers without allowing for the mortar to dry, the lower layers won’t hold up the new layers, resulting in a deformed wall. Likewise, if you keep piling on information without pausing to let it sink in, you’ll end up with a deformed understanding.1

brick walls

In other words, we have to allow time for the first set of ideas to cement before we can add the next set of ideas. This is especially true for subjects like math, science, and foreign languages, which always build upon what came before. It’s impossible to learn advanced French without knowing basic French; it’s impossible to learn calculus without knowing algebra.

Zooming in on short-term studying, a typical student cannot understand the advanced form of a new math technique before solidifying his understanding of the basic version of that technique. Likewise, a typical student cannot describe the processes that go on inside of a cell without first learning the names of all the parts of a cell. The neural connections that form an understanding of the basics must be established before a student can move beyond the basics.

Spaced repetition creates much-needed gaps between study sessions in which memories are formed and understanding is strengthened.


Ideally, we want sleep to play a role in this process. Sleep is the most significant time in which memories are solidified.1 Without adequate sleep, we struggle to remember the information we’ve been trying to learn.1 The best students use this to their advantage and spread their studying out over days.1

Obviously, many students put off studying until the day before the exam, so they can’t take advantage of sleep’s memory-enhancing powers. However, as we’ve already mentioned, there’s more than one way to cram. The less effective version of cramming is spending all of your available time in one sitting. The more effective version of cramming is taking that same amount of time and breaking it into two or more separate chunks.

Let’s imagine it’s Tuesday night, and a student has a vocabulary test on Wednesday in 5th period. The student has other homework, so he cannot devote his entire Tuesday night to studying for the vocab test, nor, as it should now be clear, should he. Rather, he should devote a small amount of time to studying vocab right at the beginning of his night, then do his other homework, then study the vocab again before bed, then study the vocab again at breakfast, and then review it one last time during lunch right before the test. That’s four repetitions! Such a student would score much better on the vocab test than a student who spent an equal amount of time in one sitting.

Using Both Brain Modes

Dr. Oakley offers another insight into the power of spaced repetition by describing the way it taps into the two different modes the brain uses for learning: focused mode and diffuse mode.1

In focused mode, we are engaged with the material, carefully examining the information, and devouring details.1 In focused mode, we are consciously manipulating the information and actively trying to figure it out.1 If the concept is difficult, however, it probably won’t makes sense the first time we look at it.1 That’s where diffuse mode comes in.

In diffuse mode, we’re not consciously thinking about the material.1 Rather, we’re thinking about something else, or relaxing, exercising, eating, or sleeping.1 During times when we are seemingly unproductive, our brains unconsciously continue trying to understand the information we’ve been looking at in focused mode.1 In other words, we can work on other things and our brains will keep plugging away in the background. Isn’t that nice?

It is nice, but let’s be clear: Diffuse mode only works if we’ve already spent plenty of time in focused mode. If we haven’t consciously wrestled with the details, then our unconscious won’t have anything to work with. If we haven’t focused intensely on the content we’re trying to learn, then we’ll get no benefit from diffuse mode.

Making Sense of New Content

Diffuse mode is a time when the details we’ve been learning find connections with ideas we already know.1 The result is that those details make more sense the next time we look at them.1 This explains why it’s common to struggle with math homework during the evening, but then discover you’ve got a better grasp of it the next day, even though all you did in between was sleep.1

Actually, understanding very difficult concepts often requires several rounds of alternating between focused mode and diffuse mode.1 This is an important fact for students to know because it normalizes “not getting it” and encourages students to try again later. The necessity of alternating between these two brain modes also helps explain why spaced repetition creates deeper understanding for students who use the strategy.

This concept also applies to my advice on last-minute cramming. Making an effort to see the content three times in a single day allows it to be learned more deeply than if it were seen for one, long chunk of time because the student’s brain gets three opportunities to toggle between focused mode and diffuse mode. A single, lengthy cram session doesn’t allow for that, so it results in a poorer understanding of the information.


Spaced repetition is also a critical part of most creative projects precisely because creativity is largely a process of alternating back and forth between focused mode and diffuse mode.1 Most of the time creativity occurs, the brain is in diffuse mode, but has been marinating in details acquired during focused mode.

Countless “light bulb moments” have come when inventors, scientists, authors, or artists were not actively engaged in their craft.3 They had spent plenty of time in focused mode without finding the insight they were looking for, only to experience their “Aha!” while out for a walk, taking a shower, or dreaming.3

For students with creative projects, such as research papers, science fair projects, or college entrance essays, this means that better ideas will come from putting in a small amount of work on a regular basis than will come from procrastinating.

Furthermore, Dr. Oakley points out that arriving at an understanding of some complex topic that’s being taught in school is always an act of creativity, even though it’s not original creativity.1 We cannot fully grasp a scientific theory or a literary allusion until our own brains see the same connections among ideas that were seen by the brains of the original creators.1 Thus, it’s essential for all students to develop strategies that enhance creativity. Spaced repetition is one of them.

Pause and Process

Although spaced repetition works very well on the scale of hours, days, and weeks, it’s also helpful on the scale of minutes. It’s all-too-common for students to take a 45-minute history chapter and simply read it straight through without pausing to process the information. Returning to Dr. Oakley’s wall-building metaphor, the brain needs time to allow new ideas to sink in before consuming more information, just as a bricklayer must allow time for the mortar to dry before adding a new layer of bricks.1

I advise all students to pause at the end of each section within their reading to reflect on what they just read. The ideal pause-and-process moment involves the following steps:

  1. Close your eyes.
  2. Summarize what you just read in your own words.
  3. Think about how it is connected to other things you know.
  4. Predict what will be said next.

Step 2 is actually a form of self-testing, which is a form of recall practice that greatly enhances memory.1 Step 3 is a creative act that requires a brief expedition into diffuse mode–something that can only be achieved if we stop reading new details for a moment.1 Step 4 is an exercise in risk-taking that increases the student’s engagement with whatever comes next.

The habit of pausing in this way also carves out a space for students to take notes on their reading. Effective notes will put steps 2-3 on paper for future reference. By summarizing sections of the passage in your own words, you’re creating a condensed study guide that makes sense to you. The act of paraphrasing and writing it down counts as another repetition, as does reviewing the notes later.

The most effective repetitions involve making physical product by writing out ideas by hand.

The Value of (Real) Breaks

We can’t pause and process if we don’t pause. It is during breaks that we can most readily tap into diffuse mode. It is in the moments between consuming information that information is digested and absorbed. The brain needs this time to strengthen nascent neural connections. There is a tangible value to occasionally not working.

The word “break,” however, can mean many different things. For some, a break is a healthy snack; for others, it is a few minutes raiding the cookie jar. For some, a break is a walk around the block; for others, it is watching videos on YouTube. For some, a break is a few minutes of quiet reflection; for others, it is a few minutes checking social media. In each of those examples, the former is a much healthier break than the latter. A real break should give the brain time to rest and recover, it should not involve stressful stimulation, and it should not harm the brain’s health. Choose wisely.

Your brain will automatically process what you’ve been learning as long as you give it time to do so. Unfortunately, modern humans typically have smart phones in their pockets that fill any gaps we find in our days. As hard as it is to not check your phone every time you have a spare moment, I strongly advise against it. If you have a little gap in your schedule, or if you find yourself waiting somewhere for a few minutes, I advise simply doing nothing. This will allow your brain to switch to diffuse mode, giving you access to all the benefits therein.


In the long run, spaced repetition keeps us from forgetting subjects we’ve worked hard to learn. In the early stages of learning, we have to revisit content frequently in order to form memories. Later, the purpose of spaced repetition shifts to memory maintenance. The goal becomes to avoid forgetting. Luckily, at this stage, we don’t have to revisit the content frequently. Rather, we can just engage with the content occasionally, giving ourselves a little reminder of what we know.

At each stage, spaced repetition increases the value we get from our efforts and prevents us from losing the value we’ve earned. No one has put it more succinctly than Brain Rules author, John Medina:

“Repeat to remember. … Remember to repeat.”2

Works Cited

1 Oakley, Barbara. A Mind for Numbers: How to Excel at Math and Science (Even if you Flunked Algebra). Penguin, 2014. Pages 11-67.

2 Medina, John. Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School. Pear Press, 2008.

3 Csikszentmihalyi, Mihaly. Creativity: the Psychology of Discovery and Invention. Harper Perennial, 1997.

Image Credits

Title Image: Leth-Olsen, Thomas. “neighbors.” Creative Commons 2.0. Text added.

Neuron: Seyfang, Mike. “neurons.” Creative Commons 2.0.

Brick Walls: Oakley, Barbara and Terrence Sejnowski. “Learning How to Learn: Powerful mental tools to help you master tough subjects.” University of California, San Diego.

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