This paper reports on a project in a mathematics course for prospective teachers, where the teacher educator modelled feedback based on formative assessment principles. We analyse and discuss the prospective teachers' responses when they are challenged to reflect from a teacher's perspective on how to use different models to compare fractions in a primary classroom setting. We find that the prospective teachers tended to use the feedback to move forwards in their teacher perspective, while some of them reflected on their uncertainty of how to use the models in a classroom. We argue that the prospective teachers got the opportunity to reflect on their own learning process.