It is in the players guide:
During the course of the season, you will receive 2 mid-term reports and 2 final grade E-mails regarding your players. The mid-term reports are simply giving you updates on how your players are performing in the classroom, giving you a chance to adjust minutes if need be. However, if any of your players fall below a 2.0 for his final grade, he will be declared academically ineligible. If this is the first semester, he will have the chance to come back just before the Conference Tournament begins, assuming he gets his grades up. If a player falls below 2.0 during the 2nd semester, he is done for the year. To avoid this, I've used this formula that I stole from Oldresorter. By allocating my Study Hall minutes this way, I've never had a player declared ineligible in 60 seasons of HD:
* Freshman: 4.0 - HS GPA x 10
* Sophomore: 3.6 - GPA x 10
* Junior: 3.2 - GPA x 10
* Senior: 2.8 - GPA x 10