Student-centered classrooms are characterized by shared responsibility, curriculum adjustment to reduce the number of topics or to increase emphasis on a subset of topics, a high premium placed on student-generated questions and investigations, and collective validation of students' ideas as a central feature of the teaching and learning process. This paper focuses on the processes of collective validation and proposes that engagement has everything to do with what students learn. This study examines privileging and other mechanisms at play over a period of 6 classroom days. How the claims and ideas of a number of students fare in the larger classroom community discourse is described and supported by brief case studies of student pairs and groups. Transcripts of interactions are included. Contains 11 references. (DDR)