As a hallmark of authentic science practices, students need to enact epistemic agency to shape/reshape the key aspects of their inquiry work as a collaborative community. This study elaborates an emergent temporal mechanism for engaging students' epistemic agency: "reflective structuration" by which members of a classroom community coconstruct ever-evolving inquiry directions and group structures as their collective inquiry work proceeds. Using an interactional ethnography method, we examined how students (n = 22) in a Grade 5 classroom coconstructed shared inquiry directions and flexible group structures to guide their sustained inquiry about human body systems over 7 months supported by a collaborative online environment. Rich data were collected to trace the work of the eye inquiry group as a telling case. With their teacher's support, students took agentic moves to construct an evolving set of wondering areas as a way to frame what their whole class needed to investigate. Flexible groups, such as the eye inquiry group, emerged and evolved in the various areas, leading to progressively deepening inquiry and extensive idea exchanges among students. Implications for research and practice are discussed.