Carmen Zurbriggen addresses a central question of educational research interest regarding the significance of school reference groups on the development of students, a question that gains particular relevance in the context of poor academic performance and selection. The author focuses on the peak of the controversy surrounding comparative and normative peer effects and critically examines the impact of the classroom and learning environment on students' academic performance, self-concept, and career aspirations before and after the transition to secondary school, using competing theoretical models. With her multifaceted findings, she significantly expands the internationally conducted debate.