* The SAT’s role as a predictor of freshman grades is quite sensitive to students’ background characteristics. Characteristics of students’ schools are particularly important, and account for a large share of the SAT’s predictive power.
* For example, SAT scores are much less predictive of collegiate grade point averages (GPAs) among same-race students from demographically-similar schools than they are in the population at large. For example, racial minorities and students from schools with high concentrations of Blacks, Hispanics, or low-education parents earned lower freshman grades than did White students from high income schools, even when SAT scores were similar.
* High school grades are equally predictive across and within demographic categories, suggesting that grade inflation does not erode the value of GPA comparisons across high schools.
(There is a good policy brief on his site that says more about this study - the bullets above are from this brief.)