Behaviour feedback forms, four to an A4 page. I use these to get parents involved in the management of student behaviour. After a student has continued to show poor behaviour despite the school behaviour policy, I set up a meeting with parents, explain the system, and from there on send home one of these every afternoon with the student. They know they must receive one every afternoon, so the student has to give it to them. I found it worked really well, especially when parents really get on board and set up rewards at home.
Hope it helps some people out there!