This study aimed to investigate the effect of school-based practicum experience on the self-efficacy of pre-service teachers (PTs) enrolled in Teacher Education Professional Diploma (TEPD) in Jordanian universities. The study followed mixed methods research. In the quantitative part, an online questionnaire was administered to 134 pre-service teachers (PTs) at the outset of the practicum program. Then it was readministered to the same sample after completing the practicum. In the qualitative part, semi-structured interviews were conducted after the practicum program to investigate the skills acquired by PTs during the school practicum and to identify the challenges, they faced during the school practicum experience. In the qualitative part, a total of 18 students voluntarily participated in the interviews. Results showed that the school-based practicum experience had a statistically significant effect on the overall mean scores of the PTs' self-efficacy in the pre-and post-applications and each study area (instructional strategies, classroom management, and student engagement). Furthermore, PTs reported several challenges during the school practicum, including the role of the academic supervisor, the cooperating school, the cooperating teacher, the nature of the TEPD program, and dealing with students.