Excellent point. Maybe a couple girls could disappear, and the officials would just assume they ran away and tell the rest that they were damned to hell anyway.
Of course, they wouldn't know the half of it...
Would you kindly click my dragons?Well, if you wanna give your characters a surviving chance, maybe the higher up staff at the school know about Slender Man and will use their knowledge to protect the children, maybe there are some places in the school that can be consider actually blessed and thus, 'protected' from Slender man to an extent.
To ramp the horror, maybe some of the faculty are actually servants of Slender Man, offering up students as sacrifices to him.
Well, that's an idea. But the headmasters are Complete Monsters, and the staff just have to follow orders or face having everyone turn against them.
My idea was that Slender Man only appears to a group of people when they subconsciously wish him into existence, usually brought on by extreme trauma and destruction of the will. In a place where every girl is held down with chairs and beaten every night, that could very well happen.
Would you kindly click my dragons?

There's this idea I've been toying around with for a while. I just discovered the Slender Man Mythos and it is AWESOME! My idea is that I want to write a psychological/cosmic horror story with Slendy. The setting is supposed to be extra Nightmare Fuel - it's an expy of the Hephzibah House, which is a private Christian boarding "school", and unfortunately, a real place. (http://formerhephzibahgirls.webs.com/)
I wonder how I could incorporate the horror that is Slender Man into a place like this?
Would you kindly click my dragons?