The moment that students sign a socially made contract, they have seen the perspectives of other members in the class, and found their decision to be of liking, placing them on more open airwaves for suggestion later in time. When students offer their rules, be open for anything, because often times they will reinvent rules and tackle topics that the teacher had not thought of yet.
(Classroom Management)
References
DeVries, R., & Zan, B. (2003). When Children Make Rules. Educational Leadership, 61(1), 64-67.