We consider tensions between collaboration, ownership, and appropriation in relation to Mikhail Bakhtin's theory of dialogism. We analyze examples of these tensions from our own research in an after-school, design research program and relate them to findings from other research that explored using collaborative learning systems in classrooms. We apply dialogism to describe factors that contribute to students' perception of these classroom experiences as ones that do or do not foster collaboration, including the culture of the classroom, the affordances of the technologies used to mediate collaboration, and the role of multivocality in the classroom. Students are using, reusing, and appropriating media in creative ways outside of their school settings while teachers are increasingly incorporating related emerging technologies such as wikis, blogs, and chat rooms into their classrooms. By understanding the factors that contribute to dialogism, educators will be better equipped to create classroom cultures and design environments to encourage collaboration among students.