This paper explores UK school students' protest activism relating to their schools' policies and practices, drawing on two datasets: 1) a newspaper analysis of media reports relating to school protests between 2000 and 2021; 2) a survey of 800 secondary school pupils in Wales. Drawing on social movements literature and adapting concepts for the school environment, we present a framework for exploring children's protest repertoires that distinguishes between institutionalised, legitimated and disruptive forms of activism. Our analysis outlines trends in pupil protest activities and explores stated motivations for protesting. We find that pupils are using a broad range of protest actions, often in combination, to voice concerns about school-based issues. Our data also suggest that pupils link their grievances to wider themes of social justice, rights, fairness and solidarity. Using principles of critical pedagogy, our study challenges hegemonic and deficit-laden ideas about children's (mis)behaviour as potential mis-readings of activism.