I have no actual knowledge concerning this, but I would bet someone repurposed most of the material from those tables. The slate for sure. Back in the 70s, some friends and I, purchased the local elementary school. Had one year to clear the lot. It was a crazy amount of work, but we made a lot of money. Took the place apart by hand. The slate chalk boards, were one of the better money makers. The gym floor brought more cash, but was ten times the work. I can’t imagine those tens thrown in a hole, horrific thought.