This study examines physical education pre-service teachers' (PTs) self-efficacy and practicum experiences as self-efficacy sources through a mixed-method approach. For the quantitative phase, a self-efficacy questionnaire was applied to 141 PTs. Results showed a stronger self-efficacy in the relationship with students and discipline promotion. Lower self-efficacy was linked to instructional strategies. Concerning the qualitative phase, eight PTs were interviewed. PTs with higher self-efficacy reported professional experiences before practicum as mastery experiences. During the practicum they highlighted as mastery experiences: classes' characteristics, planning and teaching practice; lesson observation as vicarious experiences; and post-lesson conversations as verbal persuasion. PTs with lower self-efficacy reported classes' characteristics and teaching practice as failure experiences. Lesson observation was linked to negative vicarious experiences and post-lesson conversations were associated to negative emotions and the absence of verbal persuasion. This study's results have implications inasmuch as they confirm the role of the practicum in teacher education programmes and the importance of training supervisors in the implementation and management of the training experience, thus contributing to PTs' self-efficacy development.