OAT test preparation books

Hi everyone, I am planning to study for the OAT test this summer and do the test by the end of the summer. I am researching on the best ways to study for the test and I was wondering if any one could suggest me the best books to use for this test. Also I would like to know if you think that prep courses for OAT are necessary and actually beneficial? or should I just stick to the books and practicing a bunch??

thanks everyone!!