Re:
She says that she is very careful about the heat rock, she will only let her near the heat rock, but not on it.
Yeah..right. Snakes are wild animals in a glass cage. They don't have the intuition to get off of something if it's burning them. You can't train them to not sit on the rock, it's just not done that way. When the room temp drops at night and the teacher has gone home, she's not there to "tell" the snake where to sit. A snake is going to do what a snake wants to do, and that's that.
I wouldn't have been so insistant as Mr. Ryan on the matter, however a heat rock can cause a host of problems. They're not all that safe in my opinion.
If thats the only source of heat in the enclosure, then the snake will sit on it at some point. Best to get it out now before irrepairable damage is done. You can buy a small light fixture at PetSmart/Petco and a lightbulb and hook it up to a timer and that work. Or you can get an Under Tank Heater (UTH) and install that. They're both a lot safer than a heat rock. Besides, a light also provides a better viewing enjoyment.
I wish I could find pictures of burns caused my heat rocks. I've seen a few here and there, but I don't remember where now.
But from what you're describing, it sounds as though the snake doesn't have enough places to hide and feel comfortable. It's a hell of an adjustment going to a new home, and especially one where you have a zillion people pointing at you and thumping the walls of your home.
Good ideas for a hide are a small box with a hole cut in it, a paper towel tube, a small flower pot with a hole in the bottom upside down, virtually anything she can cram herself into and feel safe. If the snake is in a kid's classroom, get the kids involved and have a contest on making a hide for the snake. Whichever hide gets the most votes, gets put in the enclosure.
But leaving an unsafe item in with a pet, in a classroom, is not only bad for the snake but creates a whole bad image for snake husbandry. Teaching kids that all they need is a heat rock is just nuts. Corns are tolerant creatures, but there's a limit to their tolerance.
Post Script: Found these after writing my post:
Hot Rock Maintenence
No Hot Rocks
Danger of Hot Rocks
Article on Hot Rock
And if those articles aren't enough to convince, ask a herp veterinarian on their experience with thermal burns in reptiles.