What do you do about behavior issues away from you?

In our house, if you get in trouble at school there is no tv at home that night. I have never had to go beyond that until Firecracker. Instead of punishing we started a reward sticker chart at school. I made it and took in the stickers and when she catches him being good or not finishing work then he gets a sticker. At 10 stickers I take him to the bookstore (which he loves to do) This works out really well for him. But you do need the teacher's participation. I would have her send him to the principal and see if that works. That seems to be my FSs biggest fear.