In the past twenty years there has been a proliferation of targeted school-based social and emotional learning (SEL) interventions. However, the lived experience of young peoples' participation is often elided, while the potential for interventions to confer unintended and even adverse effects remains under-theorised and empirically under-explored. This paper reports findings from a qualitative case study of students' participation in a targeted SEL intervention, the Student Assistance Programme. Data was generated with four secondary schools in Wales, with 41 students (age 12-14) taking part in the study. Findings indicate that students' identification for participation in the intervention and their reaction to the group composition may lead to harmful effects. Four iatrogenic processes were identified: (1) identification may be experienced as negative labelling resulting in rejection of the school (2) the label of SEL failure may serve as a powerful form of intervention capital, being employed to enhance students' status amongst peers. Possession of this capital is contingent on continued resistance of the intervention (3) targeting of discrete friendship groups may lead to the construction of intervention "outsiders" as students seek safety through the reification of pre-exiting relationships (4) students may seek to renegotiate positioning within targeted friendships groups by "bragging" about and reinforcing anti-school activities, leading to deviancy amplification.