This paper gives an account of a project undertaken by a multidisciplinary team, which included an educational psychologist, advisory teacher and behaviour consultant, to help revise and improve a school's behaviour policy and practice. At the onset, the team spent a great deal of time consulting with the teachers, parents but, above all, the students. These consultations included not only staff and class meetings but also a number of questionnaires derived from previous research. These consultations were augmented by a series of classroom observations. The students in particular provided great insight into why the original school system was so ineffective, and it was largely on the basis of their insight that a new system was devised. The paper describes the new behavioural policy and practice and the way it was introduced to the school. The success of the new system was assessed in terms of responses of teachers, parents and pupils, the effect that the new policy had on classroom behaviour, social relationships within the school, exclusions, attendance and GCSE results. The reasons for the success of the project will be discussed in relation to the recent work of Hattie into the most effective school-based interventions. (Contains 3 tables.)