This paper explores development in teacher beliefs and ideas for adaptations with respect to students who display challenging behaviour. These students have the same right to inclusive education as other students, but evidence suggest that this still is a partially unsolved issue. The study's context is an elementary school using Lesson Study as method for professional development over a four-year period. We have used content analysis and compared teacher talk during planning meetings at the beginning and end of the four years. The main findings are increased attention towards student behaviour, increased use of contextual explanations for student behaviour, a marked increase in ideas for adaptations, and ideas changing from exerting external control to engaging students in learning activities. The findings are discussed as to whether they support inclusion and how Lesson Study might have contributed.