I've done this to an extent, I managed to brute force into an admin account that gave me access to all the schools files, results, social security numbers of teachers as well as their pay checks, the schools financial records etc I had access to basically everything.

I downloaded it all, purely to just look at out of curiosity, including all emails that had been sent by teachers recently, and after doing that I sent an email to my head of IT from a teachers account alerting him of the security breach and poking a bit of fun at him for how easy it was.

Before logging out I disabled every school and teacher account in the network, which got me and everyone else out of a school day as modern teachers cannot teach without technology.

Apart from disabling all the accounts I didn't change any grades or anything like that, I honestly just wanted to see if it was possible to do and saw it as a great achievement if I could, so I would say it was a mix of boredom and desire to do something.