This study explores the arising and unfolding of class mood with a focus on the students' agentic contributions to classroom interaction. The study is based on empirical video-data that were collected in four secondary school Italian classrooms. We identified three forms of qualitatively distinct class mood, whose unfolding in classroom interactions revealed interpersonal regulation, material negotiation and resistance, respectively. By analysing the interactive dynamics through which these class mood episodes developed, we could trace the influential process of student agency, which eventually transformed the context of interaction. In conclusion, the study points out how often overlooked emotions intertwine with the cognitive work of the classroom life and its learning opportunities.