I also had a similar story. It was also early 2000s and our high school had a calendar system for each student so they could look up in which room they would have what class. 
So a friend of mine and I have setup a proxy server which would modify rooms randomly, or randomly cancel classes. In order to &quot;test out&quot; our code, we ARP+DNS spoofed the the whole school network, so anyone visiting the site internally would end up on our site.
Most students thought it was super fun that their classes were &quot;cancelled&quot; but obviously teachers didn&#x27;t approve :-)<p>It was also a couple of months away from our graduation, and we did get into pretty big trouble, where we got suspended, and had to write a letter of apology to the principal so they would allow us to graduate.