Bakhtin's (1981) concept of chronotope provides a way of viewing student participation in the classroom as a dynamic process constituted through the interaction of past experience, ongoing involvement, and yet-to-be-accomplished goals. Although the actual design and use of classroom space may be important in facilitating a participatory pedagogy, chronotopic analysis directs attention to the grounding of interaction in dynamic and shifting time-space contexts that are emergent within the students' and teacher's discursive practices. In our analyses of classroom events and conversations, we focus on the agency of the students in actively shaping the space-time contexts of the classroom, considering how particular groundings for interaction are created as they draw on past, present, and future temporal relations to explain and justify their ideas to one another. Our analyses provide insights into the contested nature of the time-space relationships in the classroom, the hybridization of time-space contexts, and the ways students enter into past, present, and future time-space contexts during collaborative work in the classroom. (Contains 1 figure.)