Research on Self-Determination Theory has shown that teachers' need-supportive behaviour is associated with student motivation and engagement. The purpose of this study is to examine the effectiveness of an intervention aimed at increasing the motivation of students with congenital and acquired deafblindness by enhancing teachers' need-supportive behaviour. To assess the intervention effect, this study follows a multiple case-study design. Teacher questionnaires were administered and video observations of teacher--student interactions were made during pre-test, post-test and follow-up phases. The results showed that teachers provided involvement most, followed by structure and autonomy support. Teachers' provision of structure and autonomy seems to improve most after the intervention. In general, teachers of students with congenital deafblindness showed larger intervention effects than teachers of students with acquired deafblindness. The results also provide indications that students' levels of engagement improved after the intervention.