This chapter considers ways in which lesson study may be introduced and sustained within the school-university partnerships that already exist within an initial teacher education (ITE) course. In particular, we describe the challenges and opportunities associated with ITE lesson study partnerships and ways in which lesson study can deepen and even transform the nature of the school-university partnership. We draw on third-generation Cultural-Historical Activity Theory (Engeström, 2001) to highlight preservice teachers' roles as 'boundary crossers' between the activity system of the university ITE course and the activity system of the school department in which they are placed. We argue that pre-service teachers, despite their inexperience as teachers, have an important opportunity to introduce the practices of lesson study that they are learning about into the schools in which they are placed. They are also able to promote approaches to lesson planning and observation that support the values of the course and thus, through mentor development, strengthen the school-university partnership more widely than the specific lesson studies carried out. We outline three models for productive ITE lesson-study partnerships, and argue that even a relatively small number of lesson-study events throughout the school year can establish the beginnings of a transformation in the school culture away from a performative focus on evaluating the teacher and towards a more productive focus on school students' learning. This, in turn, deepens the partnership between university and school by aligning both parties more closely around a shared focus on studying learning.