One of the causes of the science teacher shortage is the low enrollment in science teacher education. In the Netherlands, science undergraduates can enroll in a half-year teaching course that leads to a teacher qualification for junior secondary education. The goal is that these undergraduates continue in teacher education to obtain a full qualification. The present study investigated how self-efficacy was related to continuing in teacher education, and to commitment, perceived workload, and stress. Moreover, we investigated how mastery experiences, vicarious experiences, social persuasions, and emotional states influenced self-efficacy. Findings based on 69 science undergraduates showed that self-efficacy was positively related to commitment and negatively to workload and stress, but unrelated to continuing in teacher education. Mastery experiences and positive emotional states explained variance in self-efficacy. We call for more research that investigates all sources of self-efficacy and for more attention to preservice teachers' emotional states in research and practice.