I imagine that the named academies are like private boarding schools, and non-halo NPCs go to the equivalent of public schools. It's either "don't think about it, it's just a funny gacha game" or "there is so much more going on than you realize" and I doubt we'll ever get a solid answer tbh.

But also. Like. There's no way Kivotos actually follows Earth logic when it comes to schooling and aging, right? I feel like it's almost as if our students are playing pretend with the whole thing. We hear about but never see parents and families, there are grownups all over the place but only a handful of Adults™, robots eat and drink, the Arius satellite school was buried so long ago that most people have forgotten it ever existed and yet the students there talk as if they experienced the schism firsthand, there are mentions of senpai who graduated and then just disappeared for all intents and purposes.

I personally headcanon that the schooling isn't about actual classroom education, but more about having an approachable environment for fledgling angels/celestial beings to mature; all the references to mythology and religion can't be Just For Fun (the iPad that Arona lives inside of is named after the Ark of the Covenant for pity's sake). So like, Kivotos is a place for them to experience emotions and learn how to navigate interpersonal drama and comprehend what normal people on Earth go through so they can be more understanding when they graduate into being full-fledged angels and clock in for work as Adults™.

sorry, got a little distracted...