I give all freshmen 10 minutes of SH, and all other players 0. Just pay attention during the Midterms report, and if anyone is near or below 2.0, raise their SH significantly (by 10 or 20 points, depending on the situation).
EDIT: - I'll give JUCOs 10 minutes as well.
It works. I have 4 teams, 2 that are pretty successful,and have only had one player lose time due to grades in my memory.