In the context of the student-teaching practicum, interactions with cooperating teachers and pupils are believed to comprise the press for professional identity development, though theory-based explanations are often neglected in the literature, and findings are not always consistent. To address this issue, the authors used grounded theory to articulate a model explaining the relations among three constructs important to the process of identity development of student teachers. The findings are organized around a model that highlights the phenomenon of “negotiating who I am as a teacher”.