I'm not sure really, how the computers reset themselves. But, if you change the wallpaper, change the dock to your likings, save files, or have something in the Trash, it's all going to go back to normal, like after doing a fresh install of Panther. Any files you had saved with your last session will be gone the next time the computer is turned on. The school has some software installed that might do this for them, I think the software puts a little polar bear in the menu bar that does nothing, if you click on it. The software is hidden, so if that is it, I'm not sure what's called.
The school does the same thing with some of the windows computers in the lab. My friend will install and play his games, then next week, he'll go back to the same computer and reinstall the games and start playing them again.
With the windows computers in the classrooms, we log into them with our username and password, and we can save just about anything to them, files only. Then, you can go to a different building, log on to a different windows computer, and our files will still be there. But we can't do that with the macs, unfortunately. So, all over the campus, whatever computer a student is at, the school pretty much makes sure, you can't mess with the computers beyond repair.