This dissertation sheds light on conceptual change dynamics in a knowledge-building classroom to better understand the complex ways students' reasoning and ideas shift in conversation with other members in the classroom. Specifically, this dissertation attempts to characterize the contextual considerations that result in students converging to generative and useful models for their inquiry as part of a dynamic system. Drawing from a design-based research study intended to explore middle school students' modeling of molecular diffusion, this work explores 1) the selection and propagation mechanisms of ideas, 2) the role of the teacher in structuring classroom conversations to support students' inquiry and 3) how students' ideas and projected selves shifted in a one-on-one conversation with the facilitators in clinical interviews setting. I propose three theoretical perspectives to look at classroom dynamics and participants interactions. I turn to the field of memetics to characterize selection forces that influence the propagation, or depression of ideas. I then look at the teacher's facilitative moves as events in a dynamic system to understand the teacher's role in maintaining the conditions conducive for knowledge-building practices. Finally, I borrow the linguistics constructs of "footing" and "positioning theory" to analyze how students view themselves in clinical interviews and how it affects the knowledge they reveal. The idea's perspective help explain why ideas that might appear idiosyncratic at first persist in students' discourse, and how teacher's moves help sustain the conditions for the advancement of ideas along with the practices that emerge. This dissertation offers new analytical perspectives and methods to investigate conceptual change dynamics in similar settings. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]