Education Productivity

Active Recall and Spaced Repetition

“The act of retrieving learning from memory has two profound benefits. One, it tells you what you know and don’t know, and therefore where to focus further study to improve the areas where you’re weak. Two, recalling what you have learned causes your brain to reconsolidate the memory, which strengthens its connections to what you already know and makes it easier for you to recall in the future.”

Peter C. Brown (Make It Stick)

Minimum Effective Dose

The MED or Minimum Effective Dose is the smallest amount of input for a desired outcome. I first came across the idea of the minimum effective dose when I was reading Tim Ferriss. He gives the example of boiling water. When you boil water, you add heat until the water boils. Adding more heat doesn’t make the water “more boiled”, so it would be a waste of resources to continue to add heat once the water is boiled. The amount of heat required to boil the water is the MED. Tim was obsessed with finding MEDs for exercises to trigger hormone cascades in the body to produce specific results. Tim is a don’t-do-more-kettlebell-swings-than-absolutely-necessary type of guy and applying that idea to everything makes life way easier and does wonders for our productivity. If we aren’t doing extra work, then we have more time and energy to do other things that are important to us. Our energy and attention are finite, so using minimum necessary force is in our best interest if we want to get more things done. It’s also a widely practiced Eastern virtue for many different reasons, it’s much to better to get the same results with less effort.

“Fill your bowl to the brim and it will spill. Keep sharpening your knife and it will blunt.”

Lao Tzu (Tao Te Ching)

I like to think of learning as broken up into 2 parts: Understanding & Remembering

Understanding is to perceive an intended meaning. A good test to see if you have correctly internalized that meaning is being able to teach it to someone else and answer questions they have on the subject.

Renown American theoretical physicist, Richard Feynman, is known for many things in the world of science, but to us study geeks he’s the brilliant mastermind behind the Feynman Technique. His technique is based on the pretty simple idea that “we thoroughly understand something when we can explain it to a five year old“. If we can simplify complex ideas into elementary speech, then we have a truly deep understanding of those said ideas. Using our sophisticated understanding of a topic, we can carefully discern which parts are deemed unnecessary for an accurate conceptualization. If we don’t understand it well enough, we’ll have trouble explaining it to someone else in a simple way. This is how I was able to grow my skills quickly as a math tutor. I would constantly be explaining complex ideas in simple ways which gave me an opportunity to fine tune my understanding of the subject.

If you want to test your understanding, using the Feynman Technique is a fantastic way to see where you stand. I’ll go over other techniques for testing understanding in future posts, but one more noteworthy technique is Scoping the Subject. Scoping the subject is great for setting up an initial framework when learning new material.

To scope the subject, flip through whatever material that needs to be studied that day and pay attention to headings, bold or italicized words, words that don’t seem familiar, and any questions that are presented in the material. Start writing down what is already known about each concept/fact or start writing questions for concepts/facts that aren’t familiar. This gives our brains a fantastic starting point. Now when we study the material, our brains are going to be looking to answer the questions that came up while we were scoping the subject. We are delicate creatures and our minds need purpose. Scoping the subject gives our study session little landmarks. There are many ways to scope a subject, but I recommend creating a Mind Map. I go in-depth about mind maps and other note-taking techniques in my last post here.

   Here are a few questions to ask when testing understanding:

  • What did I just learn?
  • What are the key points?
  • Can I rephrase this in my own words?
  • Does this make sense?
  • Can I explain this to a 5 year old?

Remembering, in terms of learning and studying, is the ability to recall or recognize information that was encoded in the past. For most exams and metrics, we are expected to remember and synthesize information that we’ve previously been exposed to and the best way to do that is practice.

I’ll go into detail another time about MEDs for understanding, but as for remembering the MED lies in Active Recall and Spaced Repetition. I’ll break down each of these terms, explain the ideas the lay the foundation for why they work, and suggest different actionable techniques that can be used to learn everything and never forget.

Active recall is the scientifically most efficient and effective way to study anything. Active recall basically means testing yourself. It’s doing activities that force you to bring up the information out from the depths of your mind. When you practice active recall, you move slower (as in you cover less content), but you are less likely to forget the material that you do go over and your understanding of it will be much richer than if you used other methods.

The Forgetting Curve

Active recall and spaced repetition is nested in an idea known as The Forgetting Curve, coined by German psychologist Hermann Ebbinghaus back in the 19th century. The forgetting curve illustrates transience – the fact that our minds forget information over time.

Ebbinghaus : Drawn Like a Child (2020) – Christopher S. Mukiibi

When we first learn something, we slowly forget it over time unless we are forced to recall that information again. Every recall slows down our forgetting rate and the amount of information that can be forgotten becomes less and less. The further we are on the forgetting curve, the harder it is to recall the information but the stronger that connection becomes. My graph isn’t drawn to scale lol but the forgetting curve mimics something like this. For all you nerds out there, here’s the equation Ebbinghaus based his forgetting curve from:

You can graph this and see for yourself if you’d like

The forgetting curve can be proven by our knowledge of 2+2=4. I love using the 2+2 example with my students because most of us confidently know that 2+2 is 4. This is because we’ve had to recall 2+2 so many times that it’s made a permanent home in our long term memory.

When we first learned what 2+2 was, our brain created a neural pathway specifically made for 2+2 is 4 and every time we need to know what 2+2 is we send an electrical impulse through that pathway. The neurons in our brain are so specific, we create pathways in our brain for literally everything we do. We have more neurons in our brain than stars in the milky way galaxy! The first few times it’s going to be difficult to recall the information, but that is because the neural pathway for 2+2 is weak. Every time we fire that neural pathway, our brains decide that this specific pathway is useful for survival and it reinforces the pathway so it’s easier accessible for further use.

The forgetting curve is also supported by Neural Pruning and Long-Term Potentiation, the biological basis for encoding and retaining memory. Basically, neural pruning is our brain removing “useless” information over time to “free up space” for more “useful” information which gets strengthened through long-term potentiation. Our brains decide what’s useful and useless based on how often we have to use that information. Our brain thinks as long as we use it often then we need it for survival, and our brain is only interested in survival. It’s not so concerned with the other things we tend of value.

In a sense, the forgetting curve outlines our neural pruning rate. Once something is considered useful, then it’s strengthened (more information is retained) if it’s used multiple times over time through long-term potentiation. This is why active recall used in conjunction with spaced repetition is the most efficient and effective way to learn new information. We trick our brain into thinking that it needs this new information for survival and we use our in-built mechanisms to bring that information to the front of the line.

Ebbinghaus believed that stronger minds can retain information for longer periods of time, and thus their forgetting curve would be slower. This was the basis for his idea of Strength of Memory. We can strengthen our memory so it’s easier for us to remember information over time. I was pretty excited to read about this because it’s proof that once we become better at studying and learning we get to actually put in less work as time goes on. It’s comforting to know that the toughest times are right now and things get easier later. At least with studying and information retention, I know that’s true as long as I keep using my brain.

Active Recall vs. Passive Learning

In my opinion, the easiest way to think of Active Recall is by pulling out the information from the depths of your brain. It’s firing the neuron sequence that’s specific to the information you are trying to learn, and like the forgetting curve suggests, the more we fire that neuron sequence, the stronger that neural connection is. The stronger the neural connection is, the longer we retain the information. Passive learning is relying on cues or other aids to help pull up the information, this can also be known as recognition. I talk a little bit about the difference between recall and recognition in the 2nd part of my The Brain vs. The Mind post. Passive learning is a lot easier to practice than active recall, but it is so much less effective.

Examples of Active Recall

Practice problems. Practice problems. Practice problems. Question Based Learning (QBL) is the best way to encode information. By doing problems, our brains are framing the concepts in concrete examples. This helps us understand why we need to learn certain facts or ideas, and that why is the key to truly internalizing the information.

However, not all questions are created equal. When it comes to study efficiency and effectiveness:

Multiple Choice Questions < Fill in the Blank < Free Response

Free response problems are the most difficult, but that challenge is precisely what we need to develop. The idea of challenge being what we need to develop is known as Opponent Processing. Free response questions are least likely to give us cues to use recognition to retrieve the information, which allows us to solely rely on our recall ability.

Fill in the blank problems (without a word bank) can provide a similar experience, but the nature of the problems provide a context that allows for recognition to carry us part of the way through.

Multiple choice problems are the least effective questions to use for active recall because the incorrect options will point us in the direction of the correct answer. Additionally, as we learn we may unconsciously associate the incorrect answer choices as triggers for the right answer. Multiple choice problems provide the highest probability of recognition as the pathway to retrieve information rather than recall, and that can fool us into thinking that we understand something when we actually don’t.

This isn’t to say that multiple choice questions don’t have their place – they are extremely useful, but as a form of an active recall study technique, they fall short. If all you have are multiple choice problems, don’t throw them out! They can still be used to cover a multitude of topics. When answering a multiple choice question – answer the question but ask a few other questions too:

  • Why are the other choices incorrect?
  • What are they other choices?
  • Which topics do they relate to?
  • How are they different from the correct choice?
  • What is the opposite or inverse of this question?
  • What are some questions that could be related to the other answer choices?
  • What are the opposite or inverse of those questions?

Asking ourselves these series of questions will help us suck the juices, so to speak, from each question. Using this method could make multiple choice questions more effective than free response, but keep in mind, it’s all about how much effort we have to put in to pull up that information. The more effort required, the stronger than neural pathway gets developed and the slower we forget!

Running through it in your mind. I love doing this, because it’s low friction, it’s quick, it’s easy, and I can do it everywhere at almost anytime. Remember, the whole objective is to just get the neurons firing so if you’re just sitting in a waiting room you can ask yourself a question, you can answer it in your head, and it’ll have the same effect! I did this all the time in EMT school and one of my students practices this method as his primary method of studying for his EMT school. Don’t worry, he knows his stuff well!

Including it in a creative project. I forgot where I’ve heard this, but one of the best way to encode information to long term memory is to utilize it in a creative project. Creating something with that information will create a huge number of unique connections and that gives us many different neural pathways to retrieve the information.

I can personally vouch for this, every time I use information in a creative project I feel like I understand it on a much deeper level. I see this happen with my girlfriend and her students as well! Doing something creative with information is an opportunity to put the new info in different contexts. We get to test it out and see why it’s useful or important. No surprise though, when I use new info in any project I end up learning way more about it in the process and the emotional impact of learning these new things helps it stick with me.

Explaining it to someone else. Also known as, The Feynman Technique. According to acclaimed physicist Richard Feynman, if you can explain it to a five year old, then you truly understand the idea. Explaining things to someone else also lets you see if you have any gaps in your knowledge. This is a fantastic reviewing technique and it’s the reason why I tutoring comes to naturally to me now. When I first started tutoring, it was difficult because my own knowledge wasn’t complete, but when I started explaining things to other people I found where my knowledge holes were, filled them, and now most of the concepts I help my students with are second nature.

Using the concepts to solve a problem. This is similar to practice problems, but it doesn’t have to be an explicit discrete question. When we solve the problems, we see the reasons why knowing something is important and that reason drives us to make strong neural connections. If something is important or useful to know, then we are going to want easy access to it and solving problems is the catalyst to make it all possible.

Creating a mind map. This is a fantastic method for getting ideas out when scoping a subject. Creating the mind map helps with retention because it utilizes the new information in a creative project, but it also allows us to pull out all the information we know related to the subject. There’s the active recall element, it’s all about firing those neurons! This technique only works with the book closed, most active recall methods are done with the book closed. Making a mind map while looking at the textbook defeats the purpose. Creating the mind map organizes the information in our minds. I talk about scoping the subject, creating mind maps and other forms of information capture/externalization in my post about Note-Taking.

Use systemic consolidation or systemic expansion to deepen understanding. I also talk about this in my post on Note-Taking. Systemic consolidation is a method designed to emphasize active recall while simultaneously creating a study resource.


It involves “shrinking down” any notes that you have taken onto a smaller piece of paper. I recommend consolidating a months worth of notes into one notecard. It may seem impossible, but that challenge is the active recall element of this method. The small space forces you to examine what absolutely can’t be left out targeting the high yield information. This processes activates the filters in your mind that help you distinguish the different concepts from each other.

Systemic expansion is also a method designed the emphasize active recall, but in this process we flesh out our ideas rather than trim the fat. Systemic expansion is what I practice when I make my blog posts. When I first get an idea, it’s usually some one line small note in my notes app on my phone, but because I’m interested in teaching individuals I expand on that thought through many different mediums. The information starts in my notes app, then I move it to OneNote, which helps me organize the information a little better and I expand on it there. Once I have that higher articulated version of the information, I then expand even further in a blog post. Each of the ideas fleshed out in a blog post are then added to the book that I’m trying to write and the courses that I teach. The idea is that my understanding becomes deeper and deeper with each iteration of expansion.

Flashcards. Ahh, the tried and true method of the ages. I used to hate flashcards when I was younger, but now that I know a thing or two about studying I can see that flashcards are the way to go. Putting a question on the frontside of the card and the answer on the backside is a fantastic way to trigger active recall. The thing about flashcards is that they’re painful to get through if you don’t know the material well, but the genius of this method lies in that pain. When we feel pain, we remember things much more easily. Our brains don’t know the difference between a real threat and a perceived threat, so when we get a question wrong our body and mind will respond to that as a threat. When we flip the card to reveal the answers, our mind makes it a point to remember that just in case the threat comes back. I can go on for a while about flashcards, but know this – high quality flashcards can cover weeks of information in a matter of hours.

Make a connection to your personal life. Connecting things to our personal lives give the information an emotional charge and the more emotion we can attach to things, the easier they are to remember. Learning happens once we bring the abstract down to Earth, I like to do this in my classes. Whenever I explain an idea, I try my best to accompany it with a quick and apparent example in the real world. Don’t be afraid to make it ridiculous too, the crazier the connections the easier it will be to remember. I recommend making multiple connections to your life. If you have multiple access points to that information, then it will be easier to access especially in high pressure situations.

Review questions at the beginning and end of a study session. Active Recall is most effective when it’s done at the beginning and end of the study session. Reviewing past material at the beginning of a session prevents us from forgetting it, further solidifies the information into our long term memory, and primes our minds for the new information to come.

Putting the new information in context will also help with deepening understanding. Reviewing all the new information learned at the end of a study session also helps with retention by at least 15% (according to Spitzer), with literally no extra studying. The extra 2-5 minutes spent at the beginning and end of a study session can dramatically reduce the number of study sessions you’ll need and improves understanding. My girlfriend is currently using this method to study for the MCAT. Since she hasn’t learned all the material she needs to know for the test she has to balance reviewing old material and learning new material. To achieve this balance, she reviews all the questions that are due for spaced repetition at the beginning of the session which recalls all the past topics and places the new information in context. After reviewing those questions, she learns the new material (through other active recall methods as well) and turns that new information into practice questions which she reviews at the end of the session. Studying this way provides intentional structure to our sessions that maximize our results.

Examples of Passive Learning

There are so many different methods to studying. Each having their pros and cons. The problem with so many methods of studying is that many students love to pick the methods that appear effective and feel productive, but actually waste our time and triple our workload. Let’s start with my most despised method.

Rereading Notes or Reading the Textbook. I cannot begin to explain how much I hate this method. It seems like rereading notes or reading the textbook would be the right thing to do. After all, the information can all be found in our notes and textbook right?

A lot of students pick this method of their primary study method, but that’s working under the assumption that all we need to do is simply expose ourselves to the information. When we are studying for exams or trying to learn new things, we have to be able to recall and synthesize the information. The more difficult the exam or project, the higher the level of sophistication is required to recall or synthesize. Simply rereading notes or the textbook keeps the depth of understanding at a baseline. Only when the mind uses the information to solve problems or make connections is when things get interesting. So rather than rereading notes and reading the textbook, utilize any other active method of studying. Only use the notes or a textbook as a resource if clarification is needed. This goes for PowerPoints as well, try to only use them for clarification.

Highlighting. This one drives me crazy too. This isn’t to say that highlighting doesn’t have it’s place. I love highlighting when I read and research, but highlighting is not something to do when you are studying for an exam or a class. There way too many problems with highlighting, but only I’ll outline a couple.

1) Highlighting can easily lead to over-highlighting and it’ll be too difficult to come back later to see what is actually important. This leads to time and energy wasted just trying to figure out what needs to be learned.

2) Even if we don’t over-highlight, we have to reread the highlights which instantly doubles our work. But the reality is that we have to read outside the highlights too, so we can understand the importance of the highlight with context, which can easily triple our workload. While highlighting feels productive, it’s a trap that gives us more work that we need. Don’t give into the good feelings of pseudo-productivity, practice studying actively and keep the work at a minimum.

Only looking over solutions to problems. Not gonna lie, I did this all the time in college. Whenever I’d study for an exam I would look over my practice test, but I wouldn’t actually work through the problems. I would just look at the solutions and thinking to myself “yeah, that makes sense. I totally got this.” I can assure you that I did not “got this”. Yeah, the solutions made sense when I looked at them and I could easily recognize the concepts and practices, but the exams I took were testing my recall or synthesis abilities, not recognition. Practicing recall and synthesis enhances recognition abilities, but practicing recognition does not enhance recall and synthesis abilities. Just looking at the question does not encode the concepts. Working out the problems proves that you know how to do the problem on every level of our perception.

Listening to lectures in while sleeping. This is not how learning works. This just makes it harder to go to sleep. Additional unnecessary extraneous load is burdensome on the mind. We learn when we’re awake, we consolidate when we are sleeping.

Summarizing. Summarizing doesn’t seem to be an effective study technique for exams that require recall and synthesis as well. While a student will receive some benefit from summarizing a lecture after they’ve just heard it or summarizing a chapter after they’ve just read it, this method won’t help with inference making and incorporating the information into other higher-level cognitive tasks. If we were to summarize, we’d understand the big picture (which is helpful) but we will inevitably miss some of the details and nuances.

Spaced Repetition

“Practice that’s spaced out, interleaved with other learning, and varied produces better mastery, longer retention, and more versatility. But these benefits come at a price: when practice is spaced, interleaved, and varied, it requires more effort. You feel the increased effort, but not the benefits the effort produces. Learning feels slower from this kind of practice, and you don’t get the rapid improvements and affirmations you’re accustomed to seeing from massed practice.”

Peter C. Brown (Make It Stick)

Every time we recall information, it gets easier to recall and we forget less of it! We are also able to recall less often because our rate of forgetting is lower. This is the idea behind Spaced Repetition, which makes our studying more effective and efficient.

The point of being efficient is to get better results without having to do as much work and there is no better to do less work than to actually do less work! We aren’t designed to workout the same parts of our body all the time. If we do too many bicep curls or deadlifts or run too many miles at once, we could risk injury. We aren’t machines, humans require a refractory period, a time to relax and recover. This isn’t to say, we shouldn’t be diligent and work at something every day, but we should keep in mind that there are optimal times to work on a certain parts of ourselves. We shouldn’t try to fire the same neural pathway every second of every day. We need to give our brains time to establish and strengthen the connections.

Needs Time (2020) – Christopher S. Mukiibi

I like to think of learning like a laying a brick wall.

Each layer of the brick wall is a little tidbit of information and when we want to build a wall we have to lay each layer down in a timely manner. We place a layer of bricks, add some mortar, wait for it to dry, then add the next layer. We can’t just keep adding layers on top of layers without waiting for the mortar to dry. If we do, the entire wall easily collapses and if it doesn’t collapse, the wall will at least be crooked. Our knowledge works the same way. We have to learn a little bit of information, wait for our minds to build and strengthen the necessary connections, then build upon that knowledge once we understand the previous information. The question then becomes –

How do we know how long to wait before we build the next layer?

This is where Spaced Repetition comes in handy. The Forgetting Curve suggests that we strengthen our neural connections in direct proportion to how difficult it is to recall that information. So it would be in our best interests to recall the information right before we forget it. It’ll be hard and it takes the most effort, but it’ll give us the strongest connections with the least number of study sessions.

Thankfully, this type of knowledge has been around for awhile and there are a few established study methods and resources that Spaced Repetition and Active Recall into account. These are the best two in my opinion –

Leitner System – coined by the German Scientist Sebastian Leitner, it’s a system that’s used to practice flashcards that has integrated the principles of active recall and spaced repetition. The flashcards are sorted into groups and the different groups are reviewed over different time intervals.

The system is simple, yet effective. Initially, the student would start with all of the flashcards in Box 1. If they get the question correct, then they get to put the flashcard in the next box. If they get the question wrong, they put the question back in Box 1. Each box is reviewed in spaced intervals. When I practice the Leitner System, I review Box 1 every day, Box 2 every 3 days, Box 3 every week, Box 4 every two weeks, and Box 5 every month. I keep a study calendar that lets me know which days to study which boxes because it’s not worth the trouble remembering. This gradual increase will help me focus on the questions I don’t know and stop using valuable time on questions I already understand. The time intervals don’t have to be broken up exactly like this, I recommend adjusting your review schedule to the time frame that suits you.

Here is a variant, the incorrect answers don’t have to be sent back to Box 1. They can be sent back to the previous box. Adjust the systems as you see fit, just maintain the principles of active recall and spaced repetition.

Anki – every good pre-med already knows all about Anki lol. Anki is a study app that automates the Leitner System, but with some added benefits. When you answer a question, the app asks how difficult it was for you to recall the information. You can answer easy, good, hard, or again and depending on your answer, the app automatically sorts the questions for you. The easier the question was for you, the later Anki will ask you again. Making great Anki cards is a skill all in itself and requires its own 20 hours to get used to but I think the effort is worthwhile. Anki is cross-platform so it’s easily accessible. It’s free for most devices which is nice, but it costs a pretty penny to get it on iOS. It’s a little expensive, but it’s worth the investment when you get to knock out questions in the nooks and crannies of the day. Rather than scrolling through the same Instagram or Twitter feed, you can knock out 1 or 2 questions when you’re in line at the store or waiting in a restaurant.

When it comes down to it, the method we choose to study with doesn’t matter as long as we have the principles of active recall and spaced repetition integrated into our practices. Studying is all about firing the neural pathway in our minds and strengthening the connections that we want. Here’s a list of some peer-reviewed academic studies done on study strategies that support the claims in this blog post in case you wanna look deeper into this! Big thanks to Dr. Ali Abdaal for the curating!

Dunlosky et al 2013 – [Improving Students’ Learning With Effective Learning Techniques: Promising Directions From Cognitive and Educational Psychology. – PubMed – NCBI](…)

Karpicke 2016 – [A powerful way to improve learning and memory](…)

Spitzer 1939 –…

Butler 2010 –…

Karpicke & Blunt 2011 – [Retrieval Practice Produces More Learning than Elaborative Studying with Concept Mapping | Science](…)

4 replies on “Active Recall and Spaced Repetition”