The trick isn't to reverse any changes that the students made -- which is tough on a computer that's shared with teachers and admins -- the trick is to prevent them from making those changes in the first place. I recommend that you spend some time learning group policy, software restriction policies and similar features. Also, put your student accounts in the Users group -- not the Power Users or Administrators groups. Just putting their accounts in the Users group alone is enough to prevent them from changing much of anything except their personal settings. And you can manage their personal settings using group policy.
This was first published in July 2003