Active recall: what it is and how to study with it

Active recall means studying by trying to remember instead of rereading. You close your notes and ask yourself what the slide says, what a concept means or how to solve a problem, and only then check whether you got it right. It sounds simple, and it is. What's strange is how rarely we do it, given it's one of the best-supported study techniques there is.

The core idea is that remembering isn't just a way to check what you know: it's a way to learn it. Every time you pull something out of memory, that memory gets stronger and easier to find next time. Rereading, by contrast, shows you the material again without asking anything of you.

Here's how I use it as a final-year computer engineering student, with a real example: the random variables unit in my Probability course, which I thought I understood perfectly until I tried my first problem without notes and got nowhere.

Why active recall works

In cognitive psychology this is called the testing effect (or retrieval practice), and it's one of the most studied findings about how we learn: people who test themselves remember considerably more, days or weeks later, than people who spend the same time rereading.

Three reasons help explain it:

• Remembering strengthens the memory. The effort of searching your memory is exactly what consolidates it. If you never search for it, you never practice finding it, and on the exam that's the only thing you're asked to do.
• It shows you what you don't know. When you reread, everything looks familiar. When you try to recall, the gaps show up on their own, and you know exactly what to study again.
• It looks like the exam. You won't have the slide in front of you during the exam. Practicing without it is practicing the thing you'll actually have to do.

The catch is that it feels worse. Rereading gives you a pleasant sense of fluency; trying to remember and failing feels like, well, failing. But that discomfort is part of why it works. I go deeper into this in does rereading work?

Five ways to practice active recall

You don't need any special tool. These are the ones I use, from simplest to most demanding.

1. The blank page

Finish a topic, close everything, and write down on a blank page everything you remember: definitions, formulas, examples, how it connects to what came before. No peeking. Then open the material and compare.

With random variables, my first blank page had the definition of expected value and not much else. I'd forgotten variance, the difference between discrete and continuous, and what the distribution function was even for. That was exactly what I needed to study.

2. Cover the slide

If you study from lecture slides, this is the most practical one. Look only at the slide title and, before seeing the content, ask yourself what it should say. Then reveal it. It works especially well when reviewing, once you've been through the material once.

3. Write your own questions

As you study, jot down in the margin or in a list the questions your professor might ask: "what's the difference between expected value and variance?", "why is variance squared?" The next day, answer them without looking. Just writing the question forces you to think about what matters.

4. Explain it out loud

Explaining a topic as if to a friend who missed the lecture is active recall in its purest form, and it also shows you whether you understood it or just memorized it. It's the backbone of how I prepare for oral exams, which I wrote about in how to prepare for an oral exam.

5. Problems without the worked solution

In courses with problem sets, solving without the solution next to you is the most demanding version. Reading a worked example and thinking "yeah, I get it" is recognition. Solving it from scratch is recall and application at once.

When to do it

Active recall pays off most when you spread it out. Remembering something once is good; remembering it the next day, three days later and a week later is much better. That's called spacing, and together with active recall it's among the most solid things we know about studying.

A simple schedule that works for me:

• At the end of each topic: a five-minute blank page.
• The next day: the questions you wrote, without looking.
• A few days later: cover the slides or work a couple of problems.
• Exam week: a full past paper, timed.

Whatever you miss on each round comes back sooner. Whatever you already get right can wait longer.

Common mistakes

• Checking the answer too soon. If you're looking three seconds after drawing a blank, you never really made the effort. Give it a moment, even if it's uncomfortable.
• Staying at recognition. Multiple choice questions, or flashcards you glance at sideways, can turn into another form of rereading. Make your brain produce the answer, not pick it.
• Saving it for the end. If the first time you try to recall anything is the night before the exam, you're too late. Start with the very first topic.
• Definitions only. Remembering the definition of variance isn't the same as knowing how to calculate it or explain what it's for. Mix in questions about what, why and how.

Doing it with your own lectures

The most tedious part of all this is writing the questions. So when I built Filmina, the web app that explains my lecture slides out loud, I gave it a Review mode: it gives you a concept from the lecture with a short hint, you write whatever you remember, and only then do you see the ideas that make it up and the slides it comes from. Whatever you didn't remember comes back first next time. It's covered in practice and review.

But you don't need an app: a blank page and a bit of patience with the discomfort already get you most of the benefit.

Frequently asked questions

What is active recall?

It's a study technique where you try to remember information without looking at it, instead of rereading it. That can mean writing what you know on a blank page, answering questions or explaining the topic out loud, then comparing with the material.

Why is active recall better than rereading?

Because the effort of pulling something from memory consolidates it, and it also shows you what you don't know. Rereading feels like mastery because the text becomes familiar, but it doesn't practice what the exam asks of you: remembering without the material in front of you.

How do I use active recall with lecture slides?

Look only at the title of each slide and, before seeing the content, try to say what it should explain. At the end of a topic, close the slides and write everything you remember on a blank page, then compare.

How often should I use active recall?

There's no exact number, but it works best spread out: at the end of the topic, the next day, a few days later and a week after that. What you miss comes back sooner; what you already know can wait longer.