Thesis advisor: Katherine L. McNeill / Recent K-12 science reforms necessitate a shift in curriculum and instruction to support coherence from the students’ perspective. This coherence emerges when students see their science work as addressing and making progress on their questions and problems. Storyline curricular units afford student coherence, but teachers need support to craft coherent instruction from storyline materials. This three-paper dissertation involved research into one teacher’s storyline design work. The first empirical paper explores how one expert teacher interpreted the storyline materials as he planned for enactment. I used interaction and thematic analysis to identify key sources of tension that the teacher engaged with as he made sense of the storyline materials for epistemic agency. Three key sources of tension were: curricular coherence and student coherence-seeking; equitable participation and incremental building of science ideas; and singular or different forms of epistemic agency in discussions. Over time, the teacher grappled more deeply with these tensions and learned to leverage them to share epistemic agency with students. The second empirical paper documents how the same expert teacher designed instruction during enactment as students’ sensemaking diverged from the storyline plans. I engaged in interaction analysis to identify and describe particular episodes of storyline activity where the teacher shared epistemic agency with students in these divergences. The teacher engaged in principled improvisation related to the students’ interactive role, the science ideas they raised, and the experimental errors they experienced. Each episode involved the teacher’s efforts to work with students' divergences with an eye toward leveraging the storyline designs to share epistemic agency. The third paper, which is conceptual, provides an initial image of the Teacher-Storyline relationship. This relationship involves the teacher’s use of storyline materials to design and enact instruction with the goal to be coherent for students. The relationship concerns the teacher, the storyline materials, the participatory interactions between the two, and the subsequent planned and enacted storyline that is an outgrowth of this relationship. It has implications for ‘opening up’ curricular materials and for designing curriculum-based professional learning. / Thesis (PhD) — Boston College, 2021. / Submitted to: Boston College. Lynch School of Education. / Discipline: Teacher Education, Special Education, Curriculum and Instruction.