Well, I also haven't tried it, but I do know that having a low grade has repercussions -- it increases the weekly amount owed. (In story, they want their loan money back faster because you don't seem to be applying yourself.)
I've spent the last week trying to miss school the entire time, nothing really changes. As long as you keep attending school on test day you can just not go the other days, it'll just be slightly harder studying for the test.
