DH and I took PR class for LSAT, so not exactly the same situation as your son's. I scored in the top 2% of takers. Honestly, the class was way more helpful for DH than it was for me. He learns through hearing. I learn through working problems, so being forced to work questions and take practice exams did help me, but I probably could've done it on my own. If your son isn't disciplined enough to work problems on his own, consistently, then I'd do the class. Think of the money as an investment, and hopefully it will pay off with scholarships.
Good luck to you and your son!