One of the main characteristics of LS is live observation of lesson. The COVID-19 pandemic, however, made the face-to-face participation and live lesson observation challenging. Therefore, we propose the potential of combining LS with lesson analysis (LA) as a robust approach of teacher professional development through an online collaboration. The merged adoption could be a practical alternative at the onset of COVID-19. This study presents a case study that delves into the experiences and insights of three researchers from three countries that conducted LA collaboratively online. Analysis of a Grade 2 Mathematics lesson of a Japanese school was based on video recordings, lesson transcript and pupils’ notebooks. Each researcher provided insights on different aspects: mathematics education, bansho skills, and the relationships between teacher’s standpoint and questioning. These are found to be valuable for developing and continuing LS, particularly in the groundwork for kyouzai kenkyuu and post-lesson discussion.