One of my schools had a login system for teachers to edit their own webpages, and also access "teacher-only" things like schedules and grades. However, it (and the entire freakin' website for that matter) was so poorly coded that it never worked, and it especially never worked if you used a student account. Teachers would have to tell their kids that if they needed to look at their homework and stuff online, they needed to use the teacher's account (because the student account never worked), so essentially everyone knew every teacher's account and password. Yeah.
However, for the times that even the teacher account didn't work, I was called in (because they thought that I was a leet haxor that could get it working again). That was a mistake on many occasions to call me in. See, the website would almost randomly give administrator access to the website depending on if you were connected the school's network and if you were using a teacher account. So basically, I would try to force it to give me admin access, and would end up crashing the whole login system so that for at least a week no one could log on. All the time I swore I was "fixing" it.
One really cool thing I did over the school's public network was setting up a word document entitled "Open Me" where people could open the file, type a line, and save it for everyone else to read. Kind of like a really slow and primitive chatroom. I used a similar word document to prank a kid into thinking that the plot of National Treasure was real and took place around the school. It was fun seeing him look under bathroom sinks in the interest of finding "clues".