cleaning up

At my school we have carts of iBooks that go from class-room to class-room, and are used by whoever needs them at the time. The iBooks have an admin account, a standard teacher account, and a managed student account.

Whenever students use the laptops they always change the Desktop picture, leave files everywhere, etc, so i was tasked (unfortunatly not for money) to prevent this from happening.

As is apparent, i have a few questions.

What would be the easiest way to allow students to create and edit whatever they want, but when they are done, clean up after them? They need access to System Preferences, so locking up is not an option. I was considering writing an apple-script that runs on start-up and deletes everything that the students added, but then i ran across the problem of changing back the desktop pic -- how would i do that in applescript? Or is applescript the wrong way to go about it?

Answers or advice to any of my questions would be greatly appriciated.

At work we have the computers set up with restore disks, meaning that whenever you log out of a certain user account, that account is completely restored from a backup.

The only drawback is that you'd obviously have to save anything you wanted to keep outside of the home folder, but apart from that it works quite well.

It also takes ages to log back in for obvious reasons...