It seems like back in middle school we were pencil technicians. I was geeky, so my friends and I used mechanical pencils. We could basically field strip them and did so often when we were bored. I knew about different lead sizes (0.5, 0.7, 1.0 mm) and different models from popular brands. When shopping for school supplies I had to match up the right eraser refills, the right lead, etc. At three or four dollars each, a pencil seemed like an investment, so you just didn't “borrow” my pencil. I had loaner pencils on hand.
The Pentel Quicker Clicker was the workhorse. It was durable enough to be useful and complicated enough to keep me entertained during boring classes. It had an eraser seated in a metal clamp and a cap over the eraser, so there were all kinds of pieces to take apart. I think I remember a sort of needle in the bottom of the eraser for cleaning out lead, but I'm not sure.
A school supply tinkerer in probably fifth grade developed an entertaining activity with a normal wooden pencil. He discovered that you can take the end of a notebook spiral, bend it in parts so you had something like a hand-operated drill, and literally drill a hole through the pencil with the blunt broken end of the wire.