Prospective Primary Teachers (PPT) education requires different kinds of integrated activities to produce competence in building learning environments and, in particular, to produce conceptual change from the common ideas to the scientific one. Implicit conceptual knots of pupils are often present in PPT ideas on phenomena. Test in/out and research-based proposals as formative tools for Pedagogical Content Knowledge (PCK) seem useful to identify the learning knots of specific topics and support professional development of PPT. An in–out-test on DC electrical circuits was developed, also using the documentation of research with 7–12 year old students and administrated before and after a formative module based on research-based paths. The test-in stimulated reflection on the conceptual knots highlighted in the literature and the learning gain of the formative module emerged in test-out data analysis offering guidelines for PPT pre-service education.
