It will work. But they will be suspicious when their passwords are gone and/or new accounts are created. If you want I can add a bit on retrieving the password hash and then cracking that. It takes actually a bit less time than making a new account. Fairly easy for someone with your level of experience. Just didn't include it because it would have confused the hell out of nubs. But with that you could just log into the admin account of your schools computer.