School-age children like to test the limits of their behavior as well as the resolve of the adults in charge. Having just started kindergarten, chances are your son is trying to figure out exactly how tolerant his new teacher is. To put an end to this defiant behavior, you and the teacher need to work as a team. Schedule a meeting and bring your child along to discuss the issue. If possible, have your spouse come too, so your son sees that all the key grownups in his life are on board. Explain that his teacher is in charge during the day and that if he doesn't obey her, he won't just be punished at school, but that you'll discipline him at home as well. Ask the teacher to e-mail or call if your son acts up, so you can address the behavior and enforce consequences. Once your son realizes that he's not getting away with anything (and that he's losing TV, video game, and play privileges at home as a result) he'll most likely stop and respect his teacher's authority.