Does your school use SIMS or some other information management system? Cos if they do, why not steal some random details of a teacher or a pupil and use them for non-malicious 'fun'
My school uses SIMS, which while typing this post has given me an idea! Staff have their own Windows login for SIMS, so using the Fake Login Screen I could steal their pass's. Then again, I could just watch them type it in.
You can change the SIMS short cut when your on there account to the fake SIMS loggin screen (just change there password to "password" and they will go to the tec and say they lost there password)