In this paper we present a model for formative assessment based on peer-review workshops on MOODLE, designed by researchers of te University of Salerno and the University of Torino. The model has been implemented in the Mathematics and Mathematics education courses in Primary Education at the University of Torino. The peer-review workshops are intended to pursue the following objectives: (1) strengthening the argumentative skills of prospective teachers to direct them towards a relational view of mathematics; (2) provide them with models of formative assessment rooted in peer-review feedback managed by the university lecturer. We present an example of peer-review that intertwines effective feed-back with a relational understanding of mathematical thinking.