With evidence that formative assessment supports pupils' learning, it follows that that there is a need to develop student teachers' assessment competence. However, in some teacher education programmes, learning about pupil assessment is often relegated to a late stage. This can lead to student teachers' perceptions of assessment as an "add on" rather than an ongoing process of dialogue and feedback. This article discusses the findings of a year-long research project, in which modern foreign languages (MFL) student teachers undertook a systematic meta-reflection on formative assessment that was embedded in their year-long training course. The study draws on data obtained from an initial written reflection and three focus group discussions spread over the year. The student teachers, who were found to be generally inclined to formative practices in their teaching, progressed in their patterns of understanding, as well as in finding ways to implement formative assessment in the form of practical Assessment for Learning (AfL) strategies in the languages classroom. Their reflections and discussion in the university setting about classroom experimentation with formative assessment enabled them to go beyond the boundaries of summative orientations of assessment in schools and to adopt a new mindset towards assessment, teaching and learning. The article concludes that initial teacher education courses that focus on assessment are well positioned to support this kind of learning process.