This study utilizes Positioning Theory as a lens to analyze interactions between a teacher and her students. Using those interactions, this study seeks to better catalog and understand pervasive storylines in one teacher's secondary mathematics classroom as well as the intertwined positions of teacher and students within those storylines. Additionally, this study amplifies the voice and lens of a teacher participant to showcase the perceived relationship between her reflexive and interactive positioning of herself and students during episodes of interaction. This single case study investigates one teacher's classroom practice over four years as she engaged in professional development and learning around high-quality, core instructional practices for teaching mathematics. Video recordings of classroom lessons and video-stimulated recall interviews were analyzed to illuminate referenced storylines about the meanings made of teaching and learning mathematics in this space and the positions assumed and afforded within. This single case study provides unique insight into the evolution and evolvement of storylines and positions over time for this particular teacher while also honoring the relational and negotiable nature of positioning. Findings supported storyline development along three trajectories including those storylines and positions that remained consistent, others that dissipated, and still others that emerged over time. Additionally, findings suggest that professional development focused on pedagogical practice and student-centered instruction may support teachers in assuming more subdued, less powerful positions during classroom interactions and thus, affording students more agentic, authoritative, and sense-making positions throughout inquiry driven mathematics lessons. Finally, findings suggest that as teachers shift to consider their assumed positioning in interactions, they have the ability to suggest, offer, and restrict particular positions for students. Implications for practice and research are discussed for teachers, teacher educators, professional development facilitators, and researchers. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]