you wouldn't believe how scary computers were to most people. Once i added a batch file with the shutdown command in the startup folder of one computer, as a prank (trivially fixable by booting into safe mode) and got banned from the computer rooms because "i compromised every computer in the school" apparently.
They never discovered the rats we actually had installed on all their computers. They were still there years after I left, until they upgraded the computers.
I was in high school in the late 80s and early 90s, I'm well aware. :-)
We (a few friends and I) were basically the Novell Netware admins because our school didn't have a full-time computer tech and none of the teachers knew anything about it. We convinced them to let us help them in exchange for letting us read the manuals and tinker around, and we actually did help with problems and troubleshooting, mostly printing if I remember.
They never figured out it meant we also had access to the teacher-only folders though.
They never discovered the rats we actually had installed on all their computers. They were still there years after I left, until they upgraded the computers.