The challenge here is that you're assuming performance by race should be constant over time. Maybe that's true, maybe it's not, I think a richer analysis with wealth, parental education, english as a first language cofounders might be helpful.

Also if you want to entertain the theory that it is racial/genetic, it'd be important to do that analysis on a continuum since a lot of people who are "minority X" may be more than 50% white or there may be trends in that over time.