Well, I am currently in grad school. I took the GRE off of my own knowledge. I bought the test prep book and studied little by little everyday. I made about a 950, but I really wasn't concentrating. I had graduated Saturday and took the GRE on Monday. I wasn't into it. It was good enough to get me into my grad school. I am not a "class" kind of person, nor do I have the money. I just don't see the rationale behind someone teaching me how to take a test. I am currently perparing for the LSAT. Many lawyers that I know have provided prep test materials to me. They even told me that the classes were a waste.
The only way that I would take the class is ONLY AFTER I have taken the test WITHOUT assistance first. That way you can see a correlation between the two. If you take the class prior to testing, how would you know if you did well by your own merit or not? Even then, i would still be skeptical. If your scores don't go up, you don't get a refund, so what's the point?
Just study on your own, try your best, and pray.
Maybe someone sees differently....