After the COVID-19 pandemic, many schools have prioritised helping students recover from learning loss. To provide additional opportunities for students to catch up, some teachers have continued using fully online classes for supplementary teaching and learning activities. This case study examined the use of Visual Learning Analytics (VLA) to support teacher reflection in synchronous online mathematics instruction during a 2-month remedial programme. In this paper, we focused on a lesson in which the teacher was particularly dissatisfied due to students’ underperformance in post-class assignments. Drawing on data from a lesson recording with VLA, a teacher reflective journal, and stimulated-recall interviews, we gained insights into the teacher’s reflective process. Our findings suggested that our VLA platform not only provided the teacher with a holistic view of classroom interactions but also served as a catalyst for recalling and analysing specific teaching moments. This study provided evidence that VLA was a valuable resource for reflection, helping the teacher identify areas for improvement. By documenting the teacher’s experiences and the role of VLA in reflective practice, we showcased how the use of VLA could enhance teaching practices. The findings further offered practical implications for refining synchronous online instruction, particularly in remedial mathematics teaching, such as the need for more elaboration on examples and deeper probing of students’ reasoning.