I'm an underrepresented minority and I increased my SAT score by 200-300 from the PSAT to SAT, depending on how you want to measure the change. This was just by doing self-study with off the shelf test prep material. The classes aren't what increases your score, its the consistent structured study and ones innate potential. For some people, no amount of study is going to get them into the 90+th percentile. While others who have the capacity to do well but haven't had the best instruction over the years can cover a lot of ground with the right prep. But this is exactly what SAT is intended to measure, scholastic potential. That some people can increase scores dramatically through preparation does not indicate a failure of the test, but rather its success.