In many Western countries, there has been an emphasis on ways in which to support teachers to shift practice from traditional mathematics instruction to inquiry-based classrooms. As a form of professional learning and development, lesson study offers the potential for teachers to develop their ability to respond to students' thinking through participation in a professional learning community. Drawing on sociocultural learning theory, in this paper, we investigate how teachers in New Zealand learned to notice students' mathematical thinking. We analysed transcripts from teachers' post-lesson discussions. Our findings draw on analysis of teachers' post lesson discussions. They illustrate the ways in which teachers interacted with each other and highlight the important role of facilitators in supporting teachers to notice student thinking.