This article reports on a qualitative study that explored the experiences of eight Hong Kong teachers of academic subjects who undertook a full-time, short-term professional development course (PDC) designed to provide them with specialized knowledge and classroom skills required to teach content subjects through the English medium. Using a theoretical framework for understanding teacher identity, the study examined how these eight teachers believed the experiences of a short-term PDC shaped their ongoing identity construction, particularly upon completion of the course and subsequent return to their respective schools. Based upon in-depth interviews with participants and using methods of discourse analysis, the results suggest that while participants believed the impact of the PDC in terms of their own classroom teaching was positive, they faced significant challenges in realizing their preferred identity positions within the context of their whole school communities. The response of some participants to these difficulties indicated that their PDC experiences may have contributed to the establishment of a rigid division between different types of teachers within schools and that relations of antagonism appeared to exist between these different teacher identities. Implications for overcoming such divisions for the design of PDCs and for future research are discussed. (Contains 1 table.)