Focusing on a group of African American third graders who attend a high-poverty urban school, I explore the structure-agency dialectic within contested spaces situated in a dialogically oriented science classroom. Contested spaces entail the moments in which the students challenge each other's and their teacher's science ideas and, in the process, construct agentic science selves. Drawing on sociocultural frameworks, I demonstrate the complexities of agency within contested spaces and the ways in which contested spaces shape and are shaped by agentic moves. Using an interpretive qualitative analysis, I found that contested spaces bubble up are maintained by dialogue, and simmer down over time. In this study, children exercised both individual and collective agency in negotiating science ideas with their teacher to shape the science classroom space in favor of their own meaning making. Using dialogicality as a resource and building on their own cultural resources, the children acted as a community of learners to challenge their teacher's science ideas and, in doing so, transformed the dialogic space within the classroom. This study highlights the tensions teachers face in choosing authentic meaning making within the limits of the school day and their own science knowledge. In addition, it demonstrates the importance of providing equitable learning spaces for African American children that offer them opportunities to agentically use their own ways of being as resources for learning and becoming in science.