The worst i have done is got the teachers log -in info and went to the grading system and gave me a b in his class ... i wouldnt consider it hacking but yea...but the school i go to is quite impossible to hack and if you do try you will have secruity come in and escort you to the main office .. =S
But yet again my freind hacked the school and made the lunch computer crash and it took a week to fix it .