This study examined the reflective practice of 22 pre-service mathematics teachers (PMTs) as they performed a peer review of teaching through reflection in a group-based asynchronous online discussion forum that aimed to enhance their understanding of mathematics teaching and learning. This study addressed a crucial and infrequently explored issue within the field of online mathematics teacher education. Topic coding was employed to capture pertinent themes in the PMTs’ reflection reports with respect to content, process, and premise levels of reflection. The results indicated that the PMTs mostly focused on content reflection, followed by process reflection. Relatively few PMTs engaged in premise reflection. The reflective practice of the PMTs was developed to a certain extent, and forums are concluded to play a vital role in facilitating collaborative reflection and knowledge construction.