Class-based affirmative action: how?

[Die Neue Zeit]

How would class-based affirmative action work as a "dynamic minimum demand"? I don't think it would be fair to discriminate based on income (the liberal definition of "class"), per se.

[Dr. Rosenpenis]

My university gives students who graduated from public schools three extra points on the test that evaluates applicants. The test is out of 90 points. So that's like 3.3%, right? Pretty significant. Especially for students applying for less competitive fields.