in recent years, schools have set up School Peer Mediation (PSM) projects to curb the increase in violence and improve the school climate. This work explores an MSP programme conducted prior to the HARMOS reform in a Roman school. The programme aims to raise awareness of mediation among all 7th year students and to train mediators. More generally, the aim is to create a ‘mediation culture’ in the institution. This study is from a socio-cultural perspective and seeks to answer the question: how does this programme work in practice? Mixed methods are used to study PSM representations as well as the process of secondary mediation in teaching/learning situations. Two concepts of mediation emerge: mediation as a culture and mediation as an intervention procedure. While one objective is to create a ‘mediation culture’, teaching focuses on learning intervention procedures, which is also reflected in mediators’ practice. The question of standards and values to be built in common appears only marginally. In the field of teaching/learning, while the training gives pupils experience in tasks or role-play games, the work of supporting this experience is little or not addressed in teaching documents and rarely carried out in situ by teachers. In conclusion, this research shows that a project such as the MSP is crossed by implicit and self-esteem: one example is the tension between mediation as a procedure and mediation as a culture. These implications can give rise to pitfalls, such as the difficulty of creating a dialogical space that fosters the secondary development of experience or mediation, collaboration and the construction of common values and standards. — In recent years, several schools have developed programmes of Peer Mediation at School (PMS) to face the increase of violence and improve the school climate. This work focuses on a PMS program driven before the HARMOS reform in a French- speaking school in Switzerland. The aim of this programme is to raise awareness all 7th grade students to peer mediation and to train mediators. More generally, the goal is to create a culture of mediation in the institution. Drawing on a socio-cultural perspective, this study to address the question: how does this program work in practice? Mixed methods are used to study representations of PMS as well as the process of supporting in teaching/learning situations of mediation. Two concepts of mediation: mediation as culture and mediation as an intervention procedure. Why the goal is to create a culture of mediation, the actual practices show that priority is given to the teaching of intervention procedures, an aspect that also appears in the practice of trained peer mediators. An issue such as mutual construction of norms and values only marginally. As a teaching/learning subject matter, peer mediation as it is handled in sensitisation lessons expected to get some experiences in structured tasks or role plays. However, the secondary process stemming from this experience is little or not addressed in Pedagogical documents and reverted in the teachers’ actual practices. In conclusion, this research shows that a project like the PMS is understated by a number of implicit concepts: the tension between a mediation as a procedure and a mediation as culture shows it. Consequently, these implicit concepts may present obstacles, such as that of creating a dialogical space that favours the subsidiary of experience or collaboration and the construction of shared values and norms.