Well, Until the game is out and the official guide is out, we only have the demo guide
chapter 1, has two route, 1, compelte 3+ mission to continue and fail 3+ mission to go to other route
And looking at the list of CG on dlsite
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And description, the secondary school is for failed "student' will be used as breeder and prostitute for future power people, since the school is to train power people to fight demon, if you fail enough, you are unique that you have fire and ice potentional, so is transfered to secondary school to keep that trait.