The employment of formative assessment during teacher education contributes to the development of competencies of future educators and promotes their assessment competence. Thus, the aim of this research is to explore graduates working as teachers and their impressions about the assessment practices during teacher education and how they contribute to competence development; it also aims to analyse university teachers' subjective beliefs about this process as a basis for recommendations regarding its use during this period. We examined four Spanish graduates teaching in primary and secondary schools and three university teachers. Information was collected through semi-structured interviews, non-participant observations, and documentary analysis. We found that formative assessment during teacher education will contribute to the development of teaching competences if it is performed with clear criteria known to students and evidence is collected throughout the training period, giving proper feedback on the students' performance and promoting their participation in the assessment process.