Here's my view on it (and, understand, I fill in my own head cannon to make things more enjoyable):
I think it's an interesting concept to have one character with clear memories of the past lives (the teacher) who takes measures to "protect" those former lives (going so far as to kidnap them and possibly kill their families or caretakers). The kids have vague, at best, memories of their past lives, and many appreciate the lives they had in this new world (born rich, royal, etc), while some relent their new lives (born poor, outcast, etc) which causes a rifts between former friends. Cut from two characters with blades locked, ready to kill the other, to their previous lives assisting each other to score the winning goal or whatever else. Some may even believe the teacher and hope to return to their past lives which they sadly lost, since this new world is only a second chance, since their old selves died in their previous worlds, which only bolsters support for the "selfish" kids who want to be OP in the new world.