You're ignoring the concept of disparate impact. A facially neutral criteria can still be illegal discrimination if it has a disproportionate adverse effect on

You're ignoring the concept of disparate impact. A facially neutral criteria can still be illegal discrimination if it has a disproportionate adverse effect on a protected class. Lack of intent is not a get-out-of-jail-free card. Grades might fall into that category except that they have a demonstrable connection to the student's academic abilities. It would be much harder to prove a connection for who the student happens to be related to.