Challenging behaviour is a problematic issue for students with intellectual disability, including those in special education settings. While there is a need to address challenging behaviour in these schools, most Vietnamese classroom teachers struggle to deal with those behaviours due to their lack of effective strategies. In response, this first study was the initial part of a two-phase project that investigated the outcomes of professional development and learning for teachers and students in the Vietnamese context. The main purpose of this study was to pilot the design, research procedures, and instruments of the whole project. Participants were students with intellectual disability and challenging behaviour, and their teachers in Vietnamese special education settings. Both quantitative and qualitative data were collected to determine the outcomes of the teacher professional development and learning program through changes in the perception, understanding, level of confidence, strategies of teachers in using Function-based Intervention as well as challenging and replacement behaviours of target students. Insights obtained from this study will help determine the direction of the second phase of the project.