Agree with the other posters. I'd like to add my $.02:
1. Don't bother with textbooks. Go to the bookstore and buy a few of those "How to Run a Small Business for DumIdiots" books or something along those lines. Cost: < $30
2. Don't spend your summer taking business classes, use that time to instead read Dentaltown for plenty of real life advice on running a dental practice. Cost: $0
3. If you absolutely need to take a class to make yourself feel like you're learning, look for dental-specific CE classes on running a practice.
4. If you want to have an idea of what your CPA is doing, get a calculator and try doing a rough draft of your own taxes. The forms and instructions are free, and if you read the forms and plug in some numbers, you can learn a lot about where your money stays and goes. It's even easier with those tax programs. There are also dental-specific CE courses on doing taxes as well.