How often do students fall in battle?
Not all students fall in battle, and others do more than once during the course of the game. Falling doesn't necessarily mean that students have to fulfill a sentence. Several students can fall and be saved by Revive or Protect.
Still, it's good for some students to fall during the course of the game because it keeps players challenged. There has to be some risk involved to incentivize the students who don't participate as much. So if the game has gone on for several months and no one has fallen, make your point system stricter.