In this article, we present results from a research project in which the main aim was to understand students' decision-making processes in choosing to become a teacher and to make sense of the relationships between this process and the formation of their identity as a teacher. The study was conducted with 39 students from the Science Teacher Education Program (LCN) at the São Paulo University (USP) School of Arts, Sciences, and Humanities (EACH) in Brazil while the students engaged in a supervised practical internship. The data used in this study was collected from narratives written by the students in which they provided their reasons for selecting the LCN program and for choosing a teaching career. The analysis showed several elements contributing to their decision making and the formation of their identities as teachers, including the nature of the undergraduate program, representational models of teaching/teachers, the possibility of being an agent for social transformation, and an affinity toward natural sciences and/or education. Findings from this research offer implications for improvement of the LCN program and suggestions for designing teacher education programs to include actions for improving the teaching career as a life project for new students.