The first time i took the OAT i studied on my own using old textbooks and notes. The second time i took it i studied with my friend who was taking the DAT, we had prep materials from the summer programs we attended (I went to TEXOCOP), used the KAPLAN MCAT prep book and flashcards from another one of our friends, and I was lucky enough to know someone who was enrolled in the KAPLAN course so he gave me his log in and I used the practice test to work on timing. In my opinion the materials given by KAPLAN are very helpful, but if you can get the materials without paying for the class, i would advise to do so. My best advice is: study with (a) friend(s), practice on timing (very imprtant), sharpen up on math skills, and answer the questions you know for SURE, then when you have like 5 mins left go through and mark any answer. I have learned that you can study and study, but each time you take the test the questions are different and make reflect a particular stength or weakness you may have, you raise your score much more by not leaving any question blank!! 🙂