they made it look by the end that the group didn't actually did it 'cause of bullying but for a form for themselves to blow some steam (bad joke, but not as bad as the series)
glasses wanted to kill herself and the others, so why jump by the end, she could have shoved the last girl she stabbed and would have exploded her, the girl and the boy... with the other 2 guys highly likely dying from bloodloss.
also wtf was sensei