This paper documents the process and outcome of the development and validation of a coding scheme to analyse mathematics classroom discourse in the context of Hong Kong primary schools. The objective of this coding scheme was to systematically analyse teacher discourse behaviours before and after an intervention programme; the programme aimed to assist in-service teachers to develop conceptual and practical tools for engaging students in dialogical discourse in mathematics classrooms. This paper provides a detailed outline of what took place in designing and refining the coding scheme as well as improving its validity and reliability. The developed coding scheme can be effective for highlighting dialogic discourse, authority structures and student participation in mathematics classrooms and beyond. Consequently, it was possible to assess the efficacy of the teacher intervention programme. On the other hand, the developed coding scheme could be used to help teachers to gain a sense of efficacy over their instruction by giving them a roadmap for what they can do before and during instruction. Copyright © 2021 Routledge.