Even if magnetism and electromagnetism are generally not addressed during the formative courses in Italy, they are part of the curricular programs in primary schools. A formative learning intervention concerning electromagnetism was conducted in the context of the physics course for Prospective Primary Teachers (PPT) held at the University of Udine. In this paper are analysed how PPT address the analysis of the electromagnetic phenomena while they are facing an experimental learning path for pupils, looking to what conceptual nuclei and the learning knots are identified and re-used by them in the design of their own learning path.