Hi,
I took a Kaplan prep course during the spring semester of my junior year. I took the April MCAT so I could apply for Early Decision. The MCAT is the type test where some serious study habits are going to be necessary whether you take the prep course or not. I paid $1500 for the course which took up six three hours a night, two nights per week and four saturdays leading up to the test. I made the mistake of thinking that amount of "seat time" would get me the score I wanted. Since I was also taking a full course load, I neglected to study the required material that comes with the course. Still, Kaplan projected my score to be about 31, and of course I was pleased.
I took the test in April, and in June was quite disapointed with my 24N.
Long story short...I spent six weeks during the summer doing nothing except studying the books that came with the Kaplan course. I studied 8 hours a day, 6 days a week for six weeks. I took the August MCAT, made a 27P and got into my top choice of school (Mercer School of Medicine).
My opinion is, study on your own. You'll save money and not waste time. It's like any other college course...you can't work at your own pace because the instructor has to keep stopping for others. Likewise, if you don't get something, you hold everyone else up. And who do you think teaches the courses? It is largely unqualified graduate students. If you make an 11 or greater on any section of the MCAT, you are eligible to teach for Kaplan in that section. Good luck!