the bus driver pretty much used tunnels as gateways to transport all across the world, pretty much the only one among them that could do this, to designated stops on his list given to him by the headmaster who along with the other dark lords marked down each group of creatures that agreed to their plan. which was pretty much 99% of the monsters out there because they wouldn't want to cause an incident with the dark lords. They told them to expect a ride on the specified date of the start of school. of course that was the first time round, since this has now been going on for a while now. aka why humans don't really know anything about monsters anymore, they have started to keep track of monsters and most are pre-signed up before or after they was born in order to prepare. in terms of schooling this school does Highschool and College related courses/classes and by the end they will pretty much be able to go work in the human world and live how they wish in a peaceful secret life.

Granted Witches and Magicians could probably easily get off living in the human world without help since they don't have a monster from. they mostly just need to learn how to control their magic powers. There have been cover stories prepared for a lot of situations. In terms of your character who lived with regular human parents as foster parents, one such thing would be they would mysteriously come across a flier for the school that's filled with enticing information to attract their attention like it being entirely free, and more, without mentioning anything about the supernatural, these filers only given to those in similar situations then after it's done it's job it would mysteriously vanish as if it never existed, of course all handy work by a special squad of monsters who's entire job is to deal with such things.

which is one reason why they don't get schedules until at the school for if their human parents seen it, it might start to causing questions about things like the 'Human Social Studies" and some other things that could of been on the schedule which they may have in the future depending how far this roleplay gets. Especially since some monsters out there are half-breeds. actual half-breeds that are very unique mutations, who don't have complete monster forms, its more like partial.