Regarding the correlation between income and tests scores, I am surprised that nobody has brought up the much higher rate of accommodations that wealthy kids get. There are wealth school districts in which 1/4 or more of the students have one type of accommodation or another for test taking. Wealthy kids also take the tests more often.
So, for example, one of the wealthiest schools districts in Illinois (perhaps the wealthiest?), New Trier, has about 1/4 of its students with accommodations for their tests, including extra time, etc, and on average, every student takes the ACT three times (one kid took it 13 times!).
As for prep, most of the people here are talking about outliers. Kids who get 1500 on their test without prep will not benefit much from prep. My kid did not do any real prep and did very well on her SATs.
However, kids who are getting 800-1200 and so forth can boost their scores by 200-300 points if they get private prep lessons. A kid who get 1200 on their first try may not be able to get 1520 with lessons alone, but give them lesson, extra time, and three tries, they can get around 1500, especially with super-scoring.
The SAT does not test innate abilities. It is nothing more than a test of whether students have a certain set of knowledge. It is a repeat of the tests which the students have taken over their previous high school years, but with a different methodology. As such, it does not provide much information on a students academics beyond that which is provided by the GPA.
Success at college courses requires the same set of skill and competencies which were required to succeed at high school classes. There is no requirement that a students engage in a series of standardized multiple choice tests.
Also, there are a large number of very smart, very talented people, who are able to do school work, produce amazing essays, research papers, and can deal with short, relatively low stake tests. However, test anxiety is a real thing, and is pretty common.
As for SAT leveling the playing field - that makes absolutely no sense.
Research has shown that Wealthier kids have extra help preparing for the tests, have better conditions under which to study for the tests, have more opportunities to take the test, are much more likely to have accommodations, needed or not, and are taking the tests in much better conditions. With all those advantages that the children of the wealthy have, how exactly can SAT tests be "leveling the playing field?
I do not find the argument that Freddie deBoer brings, which is that all of the factors used in admissions are unfair, but he thinks that the SAT scores are the least unfair. “I think that it’s not as bad as the rest” is not a good recommendation for the inclusion of anything in any decision making.