In the Psychiatric Unit of the Modelo Prison, Barcelona, a physical education programme is carried out annually with the participation of University of Barcelona (UB) students. In this context, we carried out a study based on service-learning parameters. The aim of the study was twofold: to determine the impact on inmates of the physical education programme that was undertaken with university students; and to assess what university students' learnt in the prison-based socio-educational intervention programme. This paper describes the context of the research and the methodological basis of service learning. The qualitative tools to gather the information were: two focus group; a semi-structured interview with a representative of the unit's guards; and the students' field dairy. We present results that demonstrate the impact of the physical, sports activity on the socialisation of inmates, in terms of aspects such as communication and personal skills. The results also show the effect of the programme on the university students' learning processes, particularly with regard to the contextualisation of learning.