I used to have a standing agreement with the kids for when we practiced.

If they could ever punch, kick, or joint lock me hard enough to make me say "ow" during practice, or tag me in the head, they get to be in charge and could pick whatever they wanted to do for the rest of the class that day.

That gave them a big incentive to improve.

I heard from the mom that the kids would talk about that when they got home, and they would spend the week planning how they would get the better of me at the next practice. "I almost got him, mom!" Haha.