Yeah, this is interesting, and it's close to my experience. Just by working through the questions in the official SAT practice booklet a couple weeks prior to the test (which I think was "free" upon signing up), and learning a couple lessons from my first sitting (set a faster pace and guess rather than leaving questions blank), I probably raised my score by 300 points into the 1400+ band on my second sitting. An instructor could easily teach those lessons in a single prep session that starts with a short mock test.

The hard-core, months-long, daily prep courses for super-high-achievers seem like extreme overkill. The kids who need that are probably the ones in the 700-900 range, who need to learn a baseline level of math and English for the first time (of course, if that were possible, it would have already happened in school).