Retrieval practice is the name for deliberately pulling information out of memory: answering a question, recalling a definition, explaining something without notes. Its effect on learning is often called the testing effect.
The illusion of rereading
Rereading has a trap built in. The second time you read something, it feels familiar, and that familiarity feels like knowledge. Psychologists call it an illusion of fluency.
But recognising something when it is in front of you and being able to produce it when it is not are different abilities. Rereading trains the first. Real use - in a conversation, an exam, an email - needs the second.
What the studies found
The advantage of testing over restudying has been found again and again. In a well-known review, Roediger and Karpicke described "test-enhanced learning": taking a test on material improves later memory for it more than spending the same time studying it again.
A striking example came in 2011, when Karpicke and Blunt compared students who practised recalling a science text with students who built detailed concept maps of it. Most students expected concept mapping to work better. On the later test, the retrieval group did better - including on questions that required applying the ideas, not just repeating them.
Why recalling works
Each time you successfully retrieve something, the route back to it becomes stronger and easier to use next time. Retrieval also exposes what you do not know - the moment you cannot recall a word is precise information about what needs work.
And effort matters. A recall that takes a moment of struggle strengthens memory more than one that is effortless. That is why tests feel harder than rereading and still win.
Retrieval does not need a formal test
You do not need exam papers. Small, frequent acts of recall are enough.
- Cover the answer. Look at a word, try to give the meaning, then check.
- Ask a yes-or-no question at the end of the day. "Do I still remember this morning's word?" is retrieval if you try before you look.
- Explain it to someone. Or to yourself, out loud, without notes.
- Write it in a sentence from memory. Producing a word in context is a stronger test than recognising it.
Combine it with spacing
Retrieval is most powerful when the recall attempts are spread out. Recalling a word five minutes after learning it is easy and does a little. Recalling it three days later, then a week later, is harder and does a lot. Testing yourself at widening intervals is essentially what spaced repetition is.
A practical rule
Whenever you catch yourself about to reread something, try to recall it first. Even a failed attempt helps, because the answer you check afterwards lands on a memory that is ready for it.
Thirty seconds of trying to remember beats five minutes of looking again. It feels less productive, which is exactly why most people do not do it.