In this article, we discuss an ethnographic case study of the teaching practice (practicum) experience of a student teacher, Lynn, in a university partnership school in mainland China. Drawing on Activity Theory, we conceptualise Lynn's practicum as boundary-crossing between two different activity systems: those of the school community and the university community. The impact of the tensions of the conflicting discourses between the school activity system and the university activity system on Lynn's professional identity formation is analysed. Clarke's model of teacher identity formation is further drawn upon to analyse how Lynn undertook her "teacher identity work" amidst these conflicting discourses and power relations. Based on this study, we propose that English as a foreign language (EFL) teacher preparation is more than just a pedagogical or technological task but a task deeply infused with conflicting cultural and ideological beliefs and practices. (Contains 11 notes and 1 figure.)