Foul and give them two!
Whenever a student (or teacher) does something that goes against the contract, anyone in the classroom may call a foul. Ms. Rogers may be in the middle of a lecture and someone will call a foul and it is addressed immediately. The instances that I see the most often are students making rude comments to one another or talking while the teacher is leading an activity. Students call one another out and in response Ms. Rogers 'addresses the foul' and the student that was called out has to say two positive things about the person they fouled, and they must be sincere. 'She is nice' is not an acceptable compliment and the students are really good about coming up with them. I've learned a lot about the students in the class (hobbies, subject interest) by listening to the compliments each student receives.
Ms. Rogers admitted that at first students took up a lot of class time giving out fouls, and then they realized that what was not completed in class was assigned as homework. She said that the system really fixed itself in time and it was worth the wait. I have to admit that it is a lot more pleasant for Ms. Rogers to say to a student that is being disruptive, 'check the contract' rather than screaming all class period long and it really make a difference in behavior.