Use a text editor such as notepad to edit the "simulation.ini" file in the "c:\program files\cat daddy games\school tycoon\data" folder. Locate the following lines:

PointsForOneStar=5.0f;
PointsForTwoStars=10.0f;
PointsForThreeStars=15.0f;
PointsForFourStars=20.0f;
PointsForFiveStars=25.0f;

Change all of those values to "0".