According to the article below by Steven Pinker, chaired professor of psychology at Harvard (FAS, not Education, please!), contrary to conventional wisdom, “SAT doesn’t track SES all that closely (only about 0.25 on a scale from -1 to 1),” and furthermore, the data show that “adolescents’ test scores track the SES only of their biological parents, not (for adopted kids) of their adoptive parents, suggesting that the tracking reflects shared genes, not economic privilege.” Hence, “as for Deresiewicz’s pronouncement that “SAT is supposed to measure aptitude, but what it actually measures is parental income, which it tracks quite closely,” this is bad social science.”"
As for the common claim that “tests don’t predict anything”: "all of these hypotheses have been empirically refuted. We have already seen that test scores, as far up the upper tail as you can go, predict a vast range of intellectual, practical, and artistic accomplishments. They’re not perfect, but intuitive judgments based on interviews and other subjective impressions have been shown to be far worse. Test preparation courses, notwithstanding their hard-sell ads, increase scores by a trifling seventh of a standard deviation (with most of the gains in the math component). "
While SATs do not favor the rich, ECs are starkly favorable to the rich in practice. New York City public high schools present a real-life laboratory for this comparison. The premier test-only school in New York City is Stuyvesant; the premier “holistic admissions” school in New York City is Beacon. In Stuyvesant, which has high immigrant demographics, almost half the students are poor enough to qualify for Federal reduced or free lunch. Beacon is whiter, richer, and more Manhattan (vs the poorer Brooklyn and Queens, representing more of Stuvyesant’s students). It also has more children of celebrities and politicians.
https://newrepublic.com/article/119321/harvard-ivy-league-should-judge-students-standardized-tests