My 6th grade class this year has been the most immature in all my years of teaching. One ringleader frequently coughs and is clearly fake in an effort to disrupt the lesson. The student does not cough at all in other classes. I don't know what to do as the student can just say it's a right to cough. I'm so frustrated and I didn't want to do a one-on-one yet because I'm afraid of blowing up. What would you do?