The popularity of synchronous online instruction has increased since the COVID-19 pandemic. This instructional environment has become a supplement to regular teaching and learning activities in the post-pandemic era. In this research report, we share our experiences from a design-based research project that investigated synchronous online mathematics instruction in secondary schools. Instead of focusing on specific school-based interventions, we summarise and discuss the research findings gathered throughout the project, offering implications from a researcher perspective, with the aim of benefiting a broader audience seeking to utilise this instructional environment to create additional learning opportunities for students. First, we discuss insights gained regarding the development of instructional materials to support online mathematics instruction, highlighting the potential of leveraging pre-service teachers to contribute. Second, we describe how we utilised AI tools to facilitate the analysis of extensive classroom discourse data gathered from lesson recordings. A two-stage AI–human coding strategy was proposed. Third, we reflect on implementations across multiple iterations and illustrate our suggestions for instructional improvement, such as employing AI-supported out-of-class activities and the associated guidelines. The contributions of this report include practical strategies for researchers and teachers aimed at supporting and enhancing the implementation of synchronous online mathematics instruction in teaching practices.