For example, Roediger & Karpicke  had college students study a passage of text much like they would for a class. All students were given 7 minutes to study the passage and then were randomly assigned into two groups… one group was given another 7 minutes to continue studying and the other group was given a test on what they had read. The final test of what students had learned took place after either 5 minutes, 2 days or 1 week.
The students were also asked how confident they were that they remembered what they had learned. Students who were given the extra time to study more were more confident, and did a little bit better when the final test was 5 minutes later. However, the students who took a practice test instead did much better on a test that was 2 days or a week later.
What does this mean for you? It means that spending hours staring at your notes is not as effective as being tested. Quiz yourself, quiz your classmates, write test questions and then practice answering them. It is all about training your brain to access the information and use it.
Want to learn more about the testing effect? Read the complete study: Test-Enhanced Learning