Since 2010 there has been a phased introduction of a new post-primary mathematics curriculum in Ireland entitled 'Project Maths'. This new curriculum places a greater emphasis on problem solving and on an investigative approach for students. This implies not only changes in the curriculum content, but also changes to teaching and learning approaches within the classroom. This research aims to provide teachers with a school-based professional development structure through which they can engage with the curriculum and attempt new teaching and learning strategies. This structure involves mathematics teachers engaging in lesson study as a professional development intervention and is investigated in two schools (phase 1 and phase 2 of Project Maths). Teachers engage in lesson study cycles repeated throughout the academic year and the research questions how effective an approach this may be in encouraging teachers to engage with and implement a new centralised mathematics curriculum. The research also investigates how effective an approach this may be in developing teachers' pedagogical practices. In this paper, initial findings will be discussed from teacher research meetings and interviews.