Teachers receive increasing attention as change agents within education reform policy discourses positioning their professionalism, identity, and agency as critical to implementation of reforms. However, identities either claimed by teachers or assigned by reform policies involve serious (re)negotiations on the part of teachers as they make practicality judgements in contexts changed by reforms. Using a temporal perspective of language teacher agency and dialogic conceptions of teacher identity, we explore a group of English teachers' (re)negotiation of claimed and assigned identities in attempts to transform traditional educational culture through implementation of the New English Syllabus of the People's Republic of China (PRC). The agency of teachers was clear in unfolding dialogic negotiation of tensions between a reform-driven identity of the effective English teacher, identities assigned by other interested groups and the community, teachers' individual claimed identities, and the possibilities of projected imagined identities. We conclude that when curriculum reform policies disrupt cultural and structural settings of the work of English teachers, temporal dimensions of dialogic (re)negotiation of professional identities play a pivotal role in reform enactment, and that policy makers must acknowledge and respond to these processes of (re)negotiation of teachers' professional identities.