Functional Behavioural Assessment (FBA) is identified as a research-based approach used in many Western schools to support student behaviour. This study aimed to assist Thai classroom teachers by providing a professional development and learning programme in FBA to develop an effective and efficient process to address behaviour problems and allow students to reach their educational potential. Classroom teachers participated in the professional learning programme in FBA. Various data sources including staff interviews, rating scales, observational time samples and descriptive notes were utilised. In the investigation the majority of teachers included FBA practice in their classrooms during the study and employed more positive and preventative approaches to deal with the students. This study confirmed that the opportunity to learn and practice skills during professional development was essential in supporting teachers in the task of improving student outcomes.