This chapter examines instances of material mediation that arose in the interaction of five bilingual students of an English as a second language (ESL) writing classroom. An analysis of the interaction between the learners and their teacher and among the learners reveals the importance of how materials mediate and are mediated by others within the learners’ zone of proximal development (ZPD). ZPD is at the heart of Vygotsky’s (Mind in society. Harvard University Press, 1978) sociocultural theory (SCT), which underscores the importance of providing assistance to learners to help develop abilities that are in the process of developing and are presently beyond their independent performance. It provides a framework to understand how humans internalize forms of mediation through socially, culturally, and historically situated contexts. Examples of collaborative dialogue shed light on theory in practice, offering a basis to guide further research in the area of material use and mediation.