There is a need to strengthen the theory-practice connection, particularly for early-career mathematics teachers, through effective professional development (PD) programs that integrate theory and research with the implementation of classroom practices. The current study investigates the effect of the online coaching component a hybrid practice-based-PD program that is focused on supporting teachers' facilitation of classroom discourse through observing and reflecting on their instructional practices during video-recorded classroom lessons. Participants were 18 early-career mathematics teachers who participated in a two-year Fellowship Program. Teachers' discourse instructional practice was analysed quantitatively using the PLATO observation tool. The relationship between these instructional practices and the online component of the PD was examined qualitatively through the analysis of teachers' reflections and coach's feedback during recorded coaching conversations. Findings revealed an improvement in teachers' discourse practices during video-recorded mathematics lessons. This improvement was associated with more explicit, specific references to classroom discourse in the teachers' reflections and more positive feedback from the coach during online coaching conversations. The study makes theoretical, methodological and practical contributions regarding effectiveness of practice-based PD programs focusing on classroom videos and coaching.