Recent reforms in science education call for efforts to engage students in authentic and sustained science practices. In order to engage students in authentic science practices, students need to enact epistemic agency over the processes of inquiry in line with how knowledge is constructed and practiced in the real world. A critical research challenge is to understand how student agency-driven science practices can be socially organized and pedagogically supported over time without pre-defined tasks and procedures from the teacher in classrooms. Situated in the context of Knowledge Building pedagogy, this dissertation contributes to a reflective structuration approach of science practices in which students are positioned as epistemic agents by co-constructing shared structures of inquiry with their teacher to guide ongoing knowledge building actions. This research adopted a two-phase exploratory sequential design conducted in four Grade 5 science classrooms from a public elementary school in upstate New York. The aims of this research were: (1) to explore how the teacher and her (his) students co-constructed and adapted various shared structures of inquiry to guide and sustain knowledge building practices over a school year; and (2) to understand the implementation processes of the reflective structuration approach and examine its impact. The first phase of this research consists of two exploratory case studies conducted in two classrooms with one teacher to explore how the two knowledge building communities co-constructed and adapted the structures about what the community should investigate (case study one) and how the community should carry out science inquiry (case study two). Findings from the two exploratory case studies led to the two-year design-based research in the second phase, which was conducted in two classrooms taught by another teacher to examine the implementation processes of reflective structuration and examine its impact. Rich classroom and online data were collected over each school year, including: (a) classroom observation notes; (b) video and audio recordings of whole classroom meetings and small-group sessions; (c) photos of classroom artifacts and student notebooks; (d) teacher's reflection journals recorded in Google Drive about significant activities and knowledge building progress in each science class; (e) video/audio recordings of student and teacher interviews; and (f) student online discourse records in Knowledge Forum. Qualitative analyses of rich classroom data uncovered the dynamic processes of how the knowledge building communities co-generated and adapted different types of shared structures to guide ongoing knowledge building actions as well as how reflective structuration was implemented in the classroom. Content analysis of students' knowledge building discourse in Knowledge Forum and quantitative comparison examined the impact of reflective structuration. Findings suggest that (1) with support from the teacher, fifth graders can co-construct/reconstruct shared structures of inquiry as they construct knowledge in a domain area; (2) a knowledge building community co-generates and adapts various shared structures of inquiry through multi-level reflection to monitor and position its knowledge building actions; (3) the teacher engages in sustained dual-layer lesson planning as an essential strategy to support both the improvement of collective ideas and the co-construction of shared structures; (4) the co-constructed shared structures are objectified through different classroom artifacts to inform sustained knowledge building engagement in the classroom and online; and (5) reflective structuration can lead to more productive and sustained knowledge building discourse as well as more sophisticated ideas from students.As a conceptual implication, this research sheds light on a more flexible way to sustain collaborative inquiry and knowledge building that engages students' high-level epistemic agency. Specifically, this research highlights the importance of positioning students with the epistemic agency through co-constructing shared structures of inquiry. Attending to the reflective and emergent process of structure development may help the field reconceptualize the tension between guiding structures and student agency in collaborative inquiry and knowledge building. As for the implication to educational practitioners, the reflective structuration approach can be adopted and developed as a new classroom strategy to implement long-term, collaborative inquiry and knowledge building without extensive pre-scripting. High-level issues, such as what to investigate, through what processes, by whom, can be co-structured by students with their teacher as the inquiry unfolds over time. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. 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