The evaluation of the educational gain of an experience is a current and binding issue in the field of non-formal and informal learning. In this regard, the paper
presents a diagnostic and formative evaluation model used in an experiential learning activity called “Feeling on the high seas” of the EFESP (Ecosistemi Formativi Esperienziali) association. This learning activity is planned for professionals such as teachers, educators, facilitators, psychologists and human resources experts both for their initial training and for their in-service training. The evaluation model is based on a ad hoc questionnaire for mapping the mindset below the acting with competence of the participants involved in the experiential learning activity. We will discuss main theoretical issues and the methodological implications with reference to the diagnostic and formative functions of the evaluation processes aimed at tailoring the experiential learning activity to the involved participants.