You can learn faster and remember more of what you learn by changing how you learn. I'll walk you through active recall, a simple technique proven to improve what you remember by 50%.

What is active recall?

Active recall is a learning technique where you test yourself on what you've learnt. This is different from 'passive learning' such as reading, listening and highlighting. Reading about the events in World War 2 is passive learning. Asking yourself "Why did World War 2 happen ?" is active recall.

The benefits of testing yourself come from the testing effect. According to the testing effect, when you recall information, you remember it better. The testing effect applies to everything - facts, complex concepts, motor skills. In his memory essay, Aristotle said: "exercise in repeatedly recalling a thing strengthens the memory."

In one study from 1939, students were asked to read articles and were then tested at various times before taking a final test two months later.  The results showed the longer the delay in the first test, the greater the rate of forgetting. What's surprising is once the student had taken the first test, the forgetting almost stopped. The student's scores on later tests also show little forgetting.

The Benefits of Testing Yourself

We now know testing yourself makes you remember more, but are they other benefits of testing yourself?

1. By testing yourself, you improve your ability to apply knowledge to new contexts and problem. You become more proficient in solving novel problems.
2. When you test yourself, you are able to gauge what you know and what you don't know. We are able to spot our mistakes and use feedback to improve our learning. When you re-read your notes and textbook, we fall prey to "illusions of competence". Reading leads to fluency and this tricks us to feel like we've mastered something. By testing yourself, you are clear on whether you mastered the information.
3. Testing yourself also enhances creativity. By learning better, your improved knowledge becomes the base for better problem-solving. Creativity without a good foundation of knowledge is heedless.

How does testing yourself compare with other study techniques?

1. Testing yourself is more effective than rereading. Dozens of studies show you recall 50% more information by testing yourself compared to rereading in the same amount of time.
2. While cramming is better for short term memory, you tend to forget what you learn faster when compared to testing yourself. The benefits of testing yourself kick in when you play the long game.
   
   A study in 1978 compared students who crammed with students who tested themselves. The ones who crammed had higher scores in an immediate test, but they forget faster compared to the students testing themselves. When they took another test two days later, the cramming group has forgotten 50% of what they recalled in the initial test. The retrieval group has only forgotten 13% from their earlier test.
3. Testing yourself is better than mind mapping. A study in 2011 compared different study techniques and the rates of retention. Researchers split students into 4 groups with each student learning the same material before sitting for a test. Each group learned with different methods.
   
   The first group would read the material only once.
   The second group would read the material four times.
   The third group would read the material then make a mind map.
   The fourth group would read the material once, then recall what they read.
   
   They discovered that the fourth group outperformed the other groups in both recalling facts and concepts.

Maximising the testing effect

Testing yourself is a high utility learning technique. To maximise this, you must repeat the act of retrieval again and again, in spaced-out sessions. Doing so, the recall requires cognitive effort rather than mindless rote learning.  By delaying our later reviews, we'll forget a bit and put in more effort to remember. We say we learn better when we find it easy, but research says otherwise. The greater the effort you put in to recall, the greater the retention.

Repeating your recall also strengthens the pathways your brain uses to retrieve information. When done enough, repeated recall can be a reflex. Pilots have trained in emergency situations over and over again it's a reflex to them.

How to use active recall

Most people don't use active recall as a studying method because it's difficult. However, we need to push our brains to make it grow. Like your muscles, the only way to make your brain 'stronger' is to lift heavier 'weights' . Here are some methods to test yourself while learning.

1. After learning something, close the source and try to recall what you learned. When reading a paragraph, or watching lecture videos, pause and ask yourself: "What did I just learn?". You'll be able to know which parts you understand and which parts you glanced over.
2. Practice productive note-taking. For some reason, note-taking is such a popular study technique. It feels productive, and you get to see your progress. Instead of summarising your textbooks, write the key points from memory. Once you've written down what you remembered, open the book and add the parts you've forgotten. Another way to do this is to write down questions for yourself. After learning, look at the questions and answer them.
3. Use flashcards. Flashcards are a good way to utilise both the testing effect and spacing effect. While paper flashcards are good, I'd recommend using an app like Anki.
4. Teach others. Teaching others is the best way to learn, as you need to understand the material to explain it to others. Albert Einstein said something similar about this: "If you can't explain it to a six year old, you don't understand it yourself."

Testing yourself is the fastest way to remember what you learn.  This study technique has allowed me to study less, and remember more.