I teach 600 students, K-8, at a Catholic school in Calif.....my best advice
is at clean-up time start counting from 10 down to 0. I let them know at
the beginning of the school year this is how clean-up works.....by the time
you get to 0 you expect that they will be seated in their seats and their
table will be "impeccably" clean. Don't ask how or why, but they respond
sooooo well to this game.