The development of professional identity during a short-track teacher education program is studied. This article presents how individuals with a strong background in natural sciences describe the teacher education in which they participate. Individual interviews were conducted with 6 student teachers with a doctorate in natural sciences and extensive work experience in science-related professions on 5 occasions during their teacher education. We suggest that shared ways of talking about education and teaching practice can be described as phases summed up as cautiously positive, rejection, acceptance, and complexity. It is argued that problems of development of professional identities can be understood in relation to the design of the teacher education under study, and failure to acknowledge the development of a professional identity as a science teacher among these student teachers is a question of a not unproblematic transformation of professional identities. Implications for teacher education are that the design of teacher education needs to consider a joint frame for the entire education, in particular the relation between practice and theoretical courses.