This paper discusses how implementation of Lesson Study (LS) has brought about evolving changes in the quality of mathematics classroom teaching in one Chinese primary school. The Japanese model of LS was adapted as a teacher professional development to improve mathematics teachers' teaching practices. The LS group consisted of five mathematics teachers. Data were collected through video recording of lesson observations, reflection and interviews with the teachers and selected pupils. Altogether five lessons were recorded: one each before and after commencing the Lesson Study; as well as one research lesson for each of the three Lesson Study cycles. In this study, the well-known Interconnected Model of Teacher Growth was used as the analytical framework to observe teacher change in the iterative processes of enactment and reflection between the four domains: external domain, teachers' personal domain, the domain of practice and the domain of consequence. Analysis of the results show five observed changes in teaching practices: (a) innovative use of teaching materials; (b) choice and sequencing of learning tasks; (c) empowering pupils to create questions; (d) resizing the group; and (e) better teacher engagement. These results showed that there were connections among the four domains; and the dynamic enactment and reflection shared by the most to the least experienced teachers was evident of teacher growth.