Managing a classroom means having reasonable classroom control at all times. The rules must be enforced fairly with reasonable consequences. Don't allow yourself to get angry or take unruly behavior personally. If the consequences for disrupting the class are too harsh, the students will lose respect for you. Keep your expectations for the teen's behavior reasonable. Expecting military discipline in the classroom is not realistic, and trying to enforced i will only put you, as the teacher, at a disadvantage. You don't have a military to back you up! One approach is to allow the students to create the rules for conduct.