In 7th grade, I was in the center room of a classroom block. When the teachers left the room, I completely gutted a computer of its fan, hard drive, CD drive, PCI cards, including its graphics card, and stuffed them in a safe place in my backpack and closed up the case. Nobody ever knew except the kids who were with me.
And, uh...
I think in 6th grade I put some ketchup packets on a toilet. Nobody knew about that either.
And in 7th grade biology, I would always steal stuff from kids' backpacks when they weren't looking. I was so quiet, I could slip out their notebook and zip it back up while they were sitting there.