I got a giant heavy-duty red plastic tarp with the art budget one year and
cut it up to fit all my tables. The tarps stay in a box where kids can get
them, and they know to put it down before getting out the clay. At the end of
class, they fold it in half and roll it up so all the crumbs stay inside.
MUCH EASIER than cleaning the tables after each class.
To keep clay moist, we use rubbermaid-type plastic under bed boxes. With some
wet towelling inside, the pieces stay damp for a long time. Works really well
-- just make sure the boxes are shut tight.