I will not tolerate any horseplay or misbehavior in my labs. Students who choose not to follow the rules are sent to another classroom to do bookwork after they write a note home to their parents about their misbehavior. I add a note to the bottom saying that their child will not be permitted to participate in the next lab unless the note is returned to me and signed by them. The note also states that if the student misbehaves in my labs again they will not be permitted to participate and their overall grade will reflect their lack of lab work. I have never had a student misbehave more than once.