This paper discusses the concepts which trained teachers carry into the classroom from their initial teacher education courses and argues that these outmoded concepts must be altered so that the roles which other adults play can be understood by teachers. There is a common perception that teaching is a solitary activity carried out by a trained adult with a group of learners. The reality is that there is often another adult present. To maximize the support of another adult, teachers must understand the roles of those involved and they must be prepared to manage the involvement of other adults who may not be trained teachers. The paper is set in the context of classroom assistants working in Scottish primary mainstream classrooms. It concerns the way in which teachers and other adults work together to support children with behavioural difficulties. Although the data is peculiarly Scottish, the lessons learned have a wider national and international currency, for it seeks to explain the changes necessary in teachers' thinking about collaborative working. This paper argues that continuing professional development must be provided to allow teachers already in the field to consider the effect on their professional identity produced by the presence of other adults. Most crucially, it is argued that initial teacher education must acknowledge the changes happening in mainstream classes and must include personnel and performance management training in courses for student teachers.