Collaborative forms of mathematics teachers’ professional development, such as lesson study, are integrated parts of the educational systems in many East Asian countries, while these forms are often new in Western countries. In this paper, we focus on a central role in lesson study, that of the facilitator. We compare how they talk with teachers and what they focus on in their talk in a lesson study context in Denmark and in China. We use a framework consisting of mentoring strategies and content categories; both developed empirically in a Chinese respectively a European context. Our analysis shows big differences in the facilitators’ ways of engaging in talk with teachers. One big difference is the dynamic and relational patterns in the Danish case as compared to the lengthy talk of the Chinese facilitator. We analyze these patterns deeply and argue that their differences are not only related to the fact that lesson study is new in Denmark, but also to social and cultural differences.