A 504 plan does not grant better protections than an IEP, and whoever told you it did was talking out of their butt. The one advantage that a 504 plan has is that it can follow your DS to college. But he also should be able to get a transitional 504 plan in place during his senior year that should seamlessly transfer to the college environment.

I would start here: http://www.wrightslaw.com/blog/?p=122