We focus on the concept of matter and explore how young children in urban schools bridge their spontaneous concepts and everyday experiences with scientific concepts introduced to them by children's literature information books and their teacher. The study shows how material artifacts used in a sorting activity became ideational tools—semiotic devices that promoted children's engagement with science and shaped the classroom discourse, thinking, and transactions. “Ambiguous” objects, such as a baggie with air, shaving cream, a baggie of salt that children were asked to sort, encouraged them to debate ideas about states of matter. Children used four ways of reasoning about states of matter: macroscopic properties, prototypes, everyday functions, and process of elimination. Furthermore, children's meaning making was intertwined with various socio-organizational aspects of inquiry—the ways in which children negotiated their roles within their group and in whole-class sessions, how they worked with each other, how their ideas were heard by others. We discuss how curricular and instructional approaches that do not lead children to one specific answer or way of thinking become catalysts for the creation of discursive spaces, where children and teacher engage in meaning making in the midst of ambiguity and confusion. © 2007 Wiley Periodicals, Inc. Sci. Ed92:65–95, 2008