This is a VERY good way to study. When I was an undergrad, I rarely ever studied. Well, in a traditional sense. I would essentially re teach my friends the material presented in the class. Though my lesson would be shaky at first, I would eventually be able to convey the concepts clearly and concisely. In my experience, the professors have been teaching the same material for years and years, so things that are apparent to them might not be so obvious to students. So, in being able to simplify the lessons in MY OWN words and teach it to other students, I can ensure that I fully understand a concept. Only when I couldn't clearly explain something in the class would I go back and review my notes/book until i would be able to.