From what little I know of the whole education thing -- well-off parents can spend between $10,000 and $20,000 on "SAT coaches" and classes like Kaplan. Combine this prep with inflated grades and I could get a ham sandwich into Princeton.
SATs were supposed to level the playing field, but have accomplished the exact opposite. Parents willing and able to foot the bill regularly have kids scoring higher than those unable to afford the expense.
The most you can get out of SAT prep is +60-100 combined.
I'm not saying you shouldn't do it, but the Roslyn scores are real enough, well explained by the ethnicity of the test takers.
SATs do exactly what they were designed to do: try to predict how well a student will do in college (specifically their freshman year). This is why leftists rail against the SAT because it accurately predicts that students promoted beyond their skill or benefitting from quotas will fail in disproportionate numbers.
If rich parents can hire special tutors to help their kids do better on the SATs (something I have not heard about but don't doubt in the slightest) that doesn't invalidate the test which has been proven to be quite accurate. It could be argued persuasively that rich kids will do better in college because they have had a better education, more resources, and more involved parents.
The SAT works because it's an impartial indicator (not determiner) of some unpleasant truths. And the last thing that liberals want is the truth laid bare... which is why they attack it.