Abstract Children and young people have a right to freedom of association and to have their views given due weight when they act collectively. However, when they come together in groups to engage in collective action, in school and elsewhere, they are often criticised for not being “representative” of all/other young people. The concept, while frequently cited, remains undefined and fails to incorporate how young people understand, experience and enact representation. This article presents data from an empirical study with youth activists who established a Secondary Schools Students’ Union during the Covid-19 pandemic to lobby for change in education decision-making. The study was carried out as a collaboration between two university-based researchers and two secondary school students who were founding members of the union. Drawing on focus groups and interviews with union executive members, this article presents findings that convey young people’s navigation of adults’ perceptions of their representativeness, focusing on issues of legitimacy and efficacy. Based on this study, we propose a new youth co-authored and youth-informed theory of representation that conceptualises it as immersive and mutually symbiotic and, we suggest, enables meaningful implementation of child and youth activists’ civil and political rights.