My natural reaction to that would've been to leave the school and every locker in it unlocked over the course of a weekend.

Not claiming any responsibility for it, naturally, simply observing that it had happened.

My father was the business manager for the school system - stuff like that was a bit difficult for me to get away with without weird consequences.

I was able to stay late after school, as I was close friends with one of my teachers. He would stay until 19:00 most days grading work and talking... now that I think of it, I could have pulled some great stunts.

Maybe randomizing the contents of a selection of not so random lockers... (purely for educational purposes, of course)

There was no need to pick locker locks in my school, since you could just stick a screwdriver in the small gap between locker door and frame and leverage the door over the frame (with no damage done). After I lost my locker key I used a screw driver for some years to open it; not even the paint was scratched :)