Background/purpose: This paper aims to examine school mentors' assessments on the degree of competences developed by preservice (candidate) teachers they supervise during teaching practicum (TP). Materials/methods: A descriptive and cross-sectional study was conducted with a questionnaire applied to 373 school mentors for the evaluation of competences of 989 preservice teachers studying Early Childhood Education or Primary Education degrees at the end of three TP periods conducted in schools located in one region of Spain. Results: From the perspective of school mentors, this study highlights that preservice teachers' competences are progressively developed during periods of TP in teacher education. The results show a more positive assessment of the school mentors about the development of the preservice teachers' personal competences than their professional competences. Conclusion: The main contribution of this study is the innovative approach applied to competence development in the TP, based on school mentors as the assessors.