Prevention is the best cure.
Be sure to walk around the lab. Do not sit behind a teacher workstation where students know they are not visible to you. Find out who set up the computer lab and have that person guide and train you on how the students can save their work in their own password-protected files. Be sure to learn how to shut down windows properly, return books and arrange the mouse, mouse pad and keyboard in its proper location at the end of class. Make sure that a user cannot write to or delete any files.