Imagine you’re learning Spanish. You might have a list of English words and their Spanish equivalents and there’s naught to do but sit down and memorize it.
Here’s the thing: You’ll memorize the list better if you look at the English alone then check the Spanish if needed, than if you look at both English and Spanish at the same time.
This is called the testing effect: Your memory is enhanced by forcing it to recall things, rather than simply seeing or hearing them. In other words, you can read the English/Spanish list all you want, but it’s much better to read the English and try to recall the Spanish before looking at the answer.
Likewise, it’s good to take notes during Spanish class, but it’s better to take notes after class. By forcing your memory to reproduce the lecture, you reinforce your memory of it. (That is, unless taking notes during class is the only way you’ll stay awake.)
But beware the catch: If you blow it and when looking at the English word “peaches” incorrectly recall the word “desnudos” instead of “duraznos,” you’ll have a difficult time retraining your mind to correctly ask for peaches instead of naked men.