Youth movements rose in Brazil in the past decade, fighting for equitable access to education alongside plural -- anti-capitalist, anti-racist, and feminist -- struggles. This article examines interactions by which Brazilian youth activists organise, politicise, and define who constitutes a movement. It focuses on a 2019 public hearing to defend race- and class-based affirmative action. Taking a discursive analytic approach situated within a broader ethnographic study, the findings highlight the collective nature of youth practices and identity. Youth activists shape a sense of belonging by emphasising 'we' and 'us' pronouns in a speech; develop audience co-authorship as they listen and chant together; and co-construct chants before initiating them in the crowd. The analysis contributes to understanding hybrid (on- and offline), multimodal educational practices and interactions in movements as youth articulate race, generation/age, class, and place. In doing so, youth construct collective identity and generate movement power.