How to learn? Quit studying and take a test.
This makes sense. What a test can do is focus your attention on what's important. One reason why students don't learn is that teachers do no make it clear what they want them to learn -- i.e., what will be on the test. Students are very practical -- will this be on the test?

Years ago I heard college profs argue that tests were essentially worthless. They should be avoided at all costs. Now we take the opposite viewpoint.