It's a school populated by a couple of adults and dozens, if not hundreds, of teenagers.
Hormone-crazed teenagers.
Hormone-crazed teenagers who can do things like fly, walk through walls, teleport, float around silently, have to try to be seen and are usually invisible, just mindblank people, and so on.
Hormone-crazed teenagers who can do things like fly, etc and who all have their own private rooms but only one communal shower for all genders.
If Xavier isn't mixing birth control in the food, he's an idiot.
That, or Xavier is Team Magneto-Was-Right and is just making sure there's going to be a small army of mutants in... oh, 15-20 years.