Why Learning By Teaching Works and How to Use It

Insights from Learning by Teaching Human Pupils and Teachable Agents: The Importance of Recursive Feedback by Sandra Okita and Daniel Schwartz.

Want to commit key points from this blog post to long-term memory? You can access an Anki Deck here.

Special thank-you to Andy Matuschak for pointing me to this paper.

Brief Overview of the Okita and Schwartz Paper

You have probably heard the advice that you should teach something if you really want to understand it. But does it really work, and if so, how?

Okita and Schwartz provide an extremely readable primer on the research behind Learning by Teaching and why it is so effective as a learning strategy.

They also explore a little-known benefit of learning by teaching called “recursive feedback” – feedback from watching your pupils use what you taught them. Using two separate experiments, Okita and Schwartz find that this special kind of feedback significantly improves teacher learning.

In this post, I summarize key insights from the paper on why learning by teaching works, and conclude with some thoughts on specific strategies for learning by teaching to improve your learning.

Why Learning by Teaching Works

Okita and Schwartz divide the learning by teaching process into three distinct phases: preparation (the teacher’s preparations to teach), teaching (the actual act of teaching), and observation (when the teacher receives recursive feedback by seeing the student apply what they learned from the teacher). It turns out that each of these phases contribute to the teacher’s learning.

Preparing

Preparing to teach students helps teachers learn due to three main forces:

  • Motivation: Preparation introduces strong emotions and motivation to truly understand the material and do it justice. This includes a sense of responsibility, the anticipation of a public performance, and a desire to avoid embarrassment or “looking stupid”.
  • Generation: Preparing to teach involves a “generation effect“. The generation effect means that you remember information better when you generate it from your mind rather than passively reading it. Preparing to teach is generative because you have to frequently retrieve and elaborate on information from your memory as you think about how you are going to teach your students.
  • Meta-cognitive vigilance: Meta-cognition refers to an awareness of your own thoughts. It turns out that preparing to teach generates this kind of awareness through the teacher’s self-explaining and self-generated questions as they anticipate the needs and questions of their pupils. This, in turn, helps teachers identify areas where they have conflicting knowledge or incomplete understanding.

Teaching

Three main aspects of this phase helps teachers learn:

  • Explanation. The act of teaching involves explaining ideas to others. This leads to “explanation effects” that occur from explaining ideas rather than just receiving them.
  • Question answering. Students often have questions of their teachers, which can reveal gaps in the teachers understanding or encourage the teacher to extend their understanding. In fact, Okita and Schwartz cite a study by Roscoe and Chi (2007) that found “tutees’ questions were responsible for about two-thirds of tutors’ reflective knowledge-building activity”.
  • Physiological arousal. Anyone that has experienced public speaking knows that it is a very stimulating activity that focuses your mind. As you might expect, this kind of arousal and attention improves learning.

Observing

In this phase, the teacher receives recursive feedback by watching the student apply what they learned. You might think it’s obvious that feedback improves learning, but it turns out that’s not always the case.

For example, direct feedback, where a student tells a teacher directly how well they did, can be counterproductive because people often take this kind of feedback personally, leading to “self-handicapping, learned hopelessness, or social comparison”. When this happens, the recipient of the feedback tends to adopt attitudes like, “well, I guess I’m not the kind of person who’s good at math“. As a result, they give up or opt for an easier subject. As much as we all like to believe we would receive feedback objectively and use it to our advantage, our egos often get involved, whether we like it or not.

Thankfully, recursive feedback side-steps this issue. Since the teacher is not directly receiving feedback from the student, their egos are uninvolved. Instead, they see for themselves what worked and what didn’t. No one explicitly tells them, “this is where you need to improve, this is what you did wrong”. Okita and Schwartz note that this “creates an ego-protective buffer, because the pupil rather than the tutor takes the immediate responsibility for being wrong”.

I also believe recursive feedback helps build empathy skills. A lack of empathy, in my opinion, is often a major barrier to learning and self-improvement. Think of how many people you have encountered in schools or workplaces that have tried to explain something to you, but assume an unreasonable amount of knowledge, leave out critical bits of information, or explain things in ways that are otherwise unhelpful (e.g. using tons of jargon you’re unfamiliar with)? Often these people are very intelligent, and would be far more effective if they gained some empathy.

How can we use these lessons about Learning by Teaching to improve our own learning?

The main lesson I took away from the Okita and Schwartz paper is that Learning by Teaching is not just folk wisdom. It works. So, as learners, we should try to use it wherever we can. Here are some ideas:

  • Develop a course or become a tutor. If there is a topic you really want to master, and you have enough time and resources, you can run an online or in-person course. In addition to the learning benefits, you can make some side income.
  • Observe your students. To take advantage of recursive feedback, you need to be able to see your students apply their knowledge. Use tests, presentations, or projects to see what your students learned.
  • Keep it interactive. Interaction with your students means more questions from them and, as a result, more learning for you. Okita and Schwartz note “Tutoring sessions should be arranged to limit the natural tendency of tutors to slip into didactics, which can eliminate opportunities for pupils to ask questions“. Students will often ask useful questions that help you better understand the material.
  • Write online. Writing online is a form of teaching, whether it’s blog posts, twitter, email newsletters, or something else. It also provides ample opportunity to receive valuable feedback about your work.
  • Develop a smart and interesting following. The quality of pupil questions impacts teacher learning. This means that, if you have an email list or a blog, or some other kind of online following, you learning would benefit from attracting high-quality people. Check out David Perell’s work on writing online, where he emphasizes the importance of writing for intelligent readers and leveraging their feedback to improve yourself.
  • Encourage your students to keep in touch about the projects they work on and how they applied the knowledge you taught them. Your students will appreciate this, and you’ll also get valuable recursive feedback.
  • Build things and watch people use what you’ve built. Okita and Schwartz point out that recursive feedback applies to areas other than Learning by Teaching. For example, producing products, tools, crafts, art, and then getting recursive feedback by observing how your “customer” uses it. One application of this idea that comes to mind is Agile software methodology, which relies on building software quickly, getting feedback on it as soon as possible, and constantly iterating and improving based on that feedback. If you produce something that others consume, you’ll gain by watching them use it.

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Notes on Developing Transformative Tools for Thought

Occasionally, special tools come along that amplify our minds, enabling new kinds of thought not otherwise possible. Computers, writing, speaking, and the printing press are all examples of these “Tools for Thought” that surge human potential. 

This essay from Andy Matuschak and Michael Nielsen explores whether we can accelerate the development of these kind of tools. They also provide a taste of potential tools for thought with their prototype “mnemonic medium”, an interactive post on quantum mechanics called “Quantum Country” with embedded flashcards combined with a spaced repetition system delivered through email follow-ups. 

Their essay is a must-read for anyone interested in spaced-repetition or productive learning. There are several points I found thought-provoking. I believe each of these insights indicate a need for a new Tool for Thought for flashcard development and sharing.

Spaced repetition creates exponential returns to studying

Based on Quantum Country user data, Matuschak and Nielsen estimate that devoting only 50% more time to spaced repetition after reading the essay resulted in users recalling the key points for months or years. 

In other words, relatively small investments in spaced repetition after reading an article produces outsized results – more evidence to place on top of the mountain of research suggesting spaced repetition works. 

Good flashcard development is difficult

Matuschak and Nielsen note that it takes a surprising amount of skill and time to build quality flashcards, especially for abstract concepts. This is probably a big reason why most people fail to adopt spaced-repetition tools like Anki. Since flashcard development is a skill that you develop over much time and effort, new users tend to add cards in a way that inevitably leads to frustration and failure. 

This may partially explain the efficacy of Quantum Country: the authors are experts in both quantum mechanics and flashcard development – a rare but essential combination of skills for their essay to work. 

Flashcards written by others can be useable

Some people the spaced repetition community don’t believe in using flashcards created by others, and with good reason. They’re often poorly written. They’re idiosyncratic. They’re missing crucial contextual information that you lack as someone who hasn’t read the original source material. I used to be one of these non-believers.

But the effectiveness of the Quantum Country essay suggests that shared flashcards can work well. This has benefits of saving users of the burden of flash card creation, as well as preventing new user frustration from poor flashcard building skills and poor domain knowledge.

Matuschak and Nielsen hypothesize that the quality of their flashcards is what makes this work. I agree, but I have a few more hypotheses: 

  • Their flashcards are introduced in a logical progression as users read the essay. In contrast, shared decks in Anki shuffle cards randomly and are not encoded with dependency information.
  • Their flashcards are clearly connected to a source (i.e. the essay), providing important context for the user.
  • Users learn the material before they review flashcards. This is in line with the common wisdom that flashcards don’t work if you don’t already understand the material – they are a tool for retention, not learning. Aside: is this common wisdom true? I’m not so sure. Socrates taught using Q and A, so why can’t you teach a subject entirely with flashcards? If it is possible, what are the prerequisites to making it work? 

Elaborative encoding

Matuschak and Nielsen note elaborative encoding as another learning tool shown to be extremely powerful in promoting memory. Essentially, it means connecting new ideas you want to remember with old ideas you know well, providing a fast path in your brain to new information. 

Remember this concept while developing your flashcards. Whenever you add a new card, think about what you already know well and how you can connect this to the new knowledge.

A New Tool for Thought?

Matuschak and Nielsen’s article has renewed my interest in a tool for thought idea I’ve been pondering for quite a while: a platform for collaborative flashcards development and sharing. I believe such a tool, if properly developed, can address the issues that limit the use of spaced repetition:

  • Spaced repetition practitioners currently need to develop their own flashcards, which requires a significant amount of time, domain expertise, and flashcard-building skill. There needs to be a place where experts can create shared flashcards, and there should be a proper incentive structure encouraging creators to improve these flashcards over time.
  • Flashcards are not clearly connected to original sources. Spaced repetition practitioners should be able to pull up pre-built flashcards for a source document they are working through. 
  • Current tools do not provide information that link flashcards together (other than knowing two flashcards are part of the same deck, or have the same tag). At the very least, flashcards should have a notion of “depends on” or “prerequisite to”. This would make shared decks more useful by showing the intended progression of knowledge. It would also aid elaborative encoding (e.g. examining cards you’ve reviewed and linking them up to cards “nearby” in a knowledge graph)

I strongly believe a tool like this needs to exist, as you may have guessed if you noticed the Download my Brain feature I built for this site that provides a platform for sharing my personal Anki decks. I have started work on a more generic tool for collaborative flashcard construction and sharing and will keep you posted once I have something ready for production. 

Thanks to Andy Matuschak and Michael Nielsen for the inspiration to follow this path.

If you’re interested in space repetition and techniques for productive learning, subscribe to my Spaced Repetition Newsletter. Check out my shared data science Anki decks here: Download my Brain.

The Hidden Power of Compounding (and 4 Ideas for Harnessing it)

Ways to take advantage of this powerful and often-overlooked force for improvement 

Ever wonder how successful people reach such heights? Think of a wildly successful person you admire. How did they get there? 

The typical answers are hard work, innate gifts (personality, natural ability) and luck. These factors play a role, but the most important factor is left out: they leverage the power of compounding.

What is Compounding?

For compounding to occur, only two things are required:

  • Growth: Something must be growing by some percentage each year
  • Time: The growth process happens over multiple years

You’ve probably heard of a specific type of compounding: compound interest. In this context, compounding means that growing your money by some percentage every year eventually snowballs into huge results if you give it enough time. 

For example, say you are able to earn 7% per year on your money. That doesn’t sound like a lot: if you invest $1000, that’s $70 in a year. Seems pretty modest.

Yes, you’ll earn $70 in year one, but in year 2 you earn $70 (7% of $1000) plus 7% on the $70 of additional money in your account that grew from year 1. As time passes, that 7% per year pumps out bigger and bigger piles of cash:

  • In Year 10: You’ve doubled the size of your account ($1,967)
  • In Year 20: You’ve quadrupled the size of your account ($3,870)
  • In Year 30: Your account is now almost 8 times your original investment of $1,000 ($7,612)

One lesson from this exercise is to save and invest some of your money. Your future self will thank you. 

Another lesson is the earlier you start, the better. More years means more opportunity for exponential growth. 

But there’s an interesting corollary to this exercise that is less obvious, and much more exciting: compounding isn’t just something that happens to your bank account – it applies to many other areas of life. 

“We’re all sort of blundering fools, but if you just get some rate of improvement and let it keep compounding, you can do pretty well…You always want to be on some sort of curve where you’re compounding.”

– Tyler Cowen, on David Perell’s Podcast

All you need for compounding is growth and time – there is nothing about dollars or bank accounts mentioned in that definition. If you can get some percentage growth rate in some area of interest every year, you’ll eventually reach heights you never dreamed possible.

Think about some area where you want to excel. As an example, let’s say you’re in sales. If you improved at sales 10% every year, you would be twice as good in 7 years, four times as good in 15 years ten times as good in 25 years, and seventeen times as good in 30 years. In any given year, you’re not making tremendous improvements, but over time persistence leads to tremendous outcomes.

Also, keep in mind that although 10% growth is a great rate for a bank account, who’s to say this is a good rate of growth for your sales career? Maybe a reasonable growth rate is much higher. If that’s the case, you can expect much more dramatic results. 

I believe this is how extraordinary people like Elon Musk reach rarefied heights: achieving a high growth rate in an area (e.g. managing a private space company) through intense focus and then relentlessly persisting to maintain that high growth rate over many years.

4 Ideas for Better Compounding

There are lots of ways you can compound in an area you want to improve. Look for anything that 1) gives you growth by some percentage or 2) helps you maintain that growth over multiple years. Some of the obvious ideas here include reading, taking lessons, attending talks, working with a mentor, and just simply doing work in the area you want to compound.

That being said, I have a few other tips that can both increase your percentage growth rate (ideas #2 and #3) and ensure you stick to it over the years (ideas #1 and #4). 

Idea #1 – Have a plan

The key to compounding is consistent, focused effort over multiple years. It’s hard to do that without being clear about where you want to improve. If you don’t have clear goals, you’ll forget them or lose discipline, stifling your compounding efforts.

So, I recommend writing down the areas you would like to compound over time. Check back on this list regularly (I check weekly) and make sure that every year you’re making some effort to improve your abilities by some percentage.

For example, here’s a list of areas I’m personally focused on compounding over time:

  • Data science
    • Statistics / math
    • Programming
  • Communication
    • Writing
    • Speaking
    • Sales / persuasion
  • Managing teams / project management
  • Personal brand / developing followers on my blog and email list
  • Health
  • Relationships
  • Cooking
  • Drumming

I keep a Google document of this list and keep track of specific things that I am doing within each category to propel myself forward. 

Idea #2 – Use spaced repetition

You’ve probably had this experience: you read a book or take a course and you want to retain it and apply as much as you can. Inevitably, the precious knowledge slowly exits your mind and 6 months later it feels like you didn’t learn anything in the first place.

Spaced repetition is a solution to this problem.

Spaced repetition is quizzing yourself on knowledge in increasing intervals of time. It’s extremely effective and time efficient. I have flashcards in my spaced repetition system that I just answered that I will not be quizzed on again in 2 years. This spacing allows you to hold tens of thousands of flashcards in your mind while only reviewing tens of flashcards a day. 

For more information about the science behind spaced repetition, check out this great summary by Gwern Branwen.

I have been a long-time user of spaced-repetition tools for committing things to long-term memory. During my university years, I wrote cards in Supermemo for all of my courses, and it was the secret weapon to my performance. Today, I use Anki, and it continues to be a key tool for compounding my knowledge in data science and retaining the vast amount of information required for success in the field.

I’m so excited about spaced repetition, I even have a feature on my website that I built to share my data science Anki decks with the world, organized by source: Download my Brain! I’m also running a Spaced Repetition Newsletter that will provide the latest news and links related to Anki, tips on using Anki, and ideas related to spaced repetition and productive learning.

Idea #3 – Keep a commonplace book

A commonplace book is a place where you store wisdom or interesting things you’ve read or heard from others, or have thought about yourself.  I’ve written previously about the benefits of keeping a commonplace book and a summary of my personal commonplace book system that involves a spaced-repetition-esque component (I wrote code to email myself 5 randomly selected commonplace book notes from my collection). Lots of others have written about them as well (here is a good article from Ryan Holiday, which is where I first heard about this idea). 

A commonplace book is similar to spaced repetition in that it’s a tool to help you retain more of the important things that you learn. It also provides you with a body of material you can draw from, which is particularly valuable if you are a writer. 

I personally use my commonplace book system to hold long-form wisdom that doesn’t lend itself well to flash card quizzing.

Idea #4 – Use commitment contracts

Once you have a plan for compounding in your improvement areas, you need to follow-through with that plan. Over the years I’ve tried many strategies to help deal with this issue of staying motivated and sticking to a plan, and the most effective tool I’ve found are commitment contracts. I’ve used commitment contracts to read and write more than I ever have in the past, despite being busier than ever with a full time job and a 3-year-old at home.

Commitment contracts are agreements where you commit to doing something, and failing leads to actual consequences. For example, I have a commitment contract to spend a minimum number of hours each week on various areas of interest. I track my time during the week, report back each week, and if I’m below my target I’m penalized $5. 

I have found this surprisingly effective, especially considering the low stakes. It doesn’t take much of a penalty to provide enough motivation to follow through with your targets. I think this may be tapping into our inherent loss-aversion: we are irrationally repulsed by a loss, much more than the size of the loss would indicate. Of course, you can make your failure penalties higher if you want, but I personally don’t find it necessary. 

The specific tool that I use for commitment contracts is StickK. I highly recommend it. 

Conclusion

I think these tips will help you out, but the most important point to remember is compounding only requires two things: growth and time. Growth ensures you make progress, and time is what allows you to reach heights you never thought possible. In any given year, you may not be making huge improvements, but over time your persistence leads to huge outcomes.

If you want to commit this article to long-term memory, download the Anki deck I put together for it here. If you are a user of Anki or other spaced repetition tools, you can subscribe to my Spaced Repetition Newsletter for the latest news, tips, and ideas about spaced repetition, using Anki, and improving your learning speed.

I made a speech based on this blog post that you can find here:

This is a speech version of this post from my local Toastmasters group

Spaced Repetition for Efficient Learning by Gwern Branwen

If you’re interested in spaced repetition and haven’t read it yet, Gwern Branwen’s essay is a fantastic review, including research into the benefits of testing, what spaces repetition is used for, software, and other observations. There are lots of resources here for people that want to know the research behind why spaced repetition works, including many studies on the effects of testing and the effects of spacing your learning. 

Here are a few points I found most interesting in Gwern’s essay:

People underestimate the benefits of spaced repetition: Gwern references fascinating research on how students and teachers grossly underestimate how much better spaced repetition is compared to cramming for learning. 

Spaced repetition as a tool for maintenance of knowledge, not gaining new knowledge: According to some of the research referenced in the essay, spaced repetition doesn’t teach you new skills or abilities. Rather, it just helps you maintain existing skills.

  • Skills like gymnastics and music performance raise an important point about the testing effect and spaced repetition: they are for the maintenance of memories or skills, they do not increase it beyond what was already learned. If one is a gifted amateur when one starts reviewing, one remains a gifted amateur.” 
  • I’m resistant to this idea that you can’t learn using flashcards. I agree if new flashcards are thrown at you randomly, then yes that is a very inefficient way to learn. But what if flashcards are presented to you in a specific order when you are learning them, and “advanced” cards are not shown to you until you’ve learned the prerequisite “beginner” cards? I don’t know the research on this, but this strikes me as potentially a better way to learn than reading, if the cards are formulated properly.  To my knowledge, none of the spaced repetition tools out there (e.g. Supermemo, Anki) allow for this kind of “card dependency” – if you know of a tool that does this, let me know.

Tradeoff between lookup time and mental space: A key question that you have to ask yourself when using spaced repetition is what information should I add to my spaced repetition system? Why add anything at all to it when you can just look it up on the internet?

  • The answer is that lookup costs can be large, especially for information that you use a lot. Often when you want to apply your knowledge, there isn’t enough time to look it up, or the time to look-up impedes your thinking. An extreme example of this would be trying to recall an important piece of knowledge in a job interview – good luck pulling out your phone in front of the interviewer to get the right answer.
  • To figure out what to add, you have to strike a balance with the tradeoff between lookup costs and the cost of adding the item to your spaced repetition system and reviewing it. Gwern provides a 5 minute rule as a criteria for deciding what to add: if you think you’ll spend over 5 minutes over your lifetime looking something up or not having the knowledge in your head will wind up somehow costing you more than 5 minutes, then it’s worth it to add it to spaced repetition.

Idea – dynamically generated cards: Gwern offers some interesting ideas about the possibility of dynamically generated cards. For example, having a card that teaches multiplication by randomly generating numbers to multiply. Similar ideas apply to chess, go, programming, grammar, and more.

If you’re interested in space repetition and techniques for productive learning, subscribe to my Spaced Repetition Newsletter. Check out my shared data science Anki decks here: Download my Brain.