SAT test scores are even more correlated with family income than how school grades are.
Book: The Tyranny of Merit
The SAT has not played out the way it was expected. It turns out that it doesn't measure scholarly aptitude or native intelligence independent of social and educational background. Conversely, SAT test scores are highly correlated with family income.
Average SAT scores increase at each rung on the income ladder. The chance for scoring above 1400 (out of 1600) for students who come from a family with an annual income greater than $200,000 is one in five. But for students from a family with an annual income less than $20,000, the chance is one in fifty.
While high school grades are to some extent correlated with wealth, SAT test scores are even more so. This is partly because, contrary to long-standing claims by the testing industry, the SAT is coachable. Private tutoring helps students to boost their scores.
The College Board administering the SAT claimed that the scores to its test were not affected by tutoring for years. However, it recently dropped the pretense and partnered with the Khan Academy to provide free online SAT practice. Though it perhaps was a method worth undertaking, it seemed to result in an even greater scoring gap between the privileged and the rest since, unsurprisingly, students from families with higher incomes and education levels made greater use of the online help.