Few studies have examined how professional learning communities (PLCs) engage in collaborative inquiry over multiple years. This dissertation describes how a PLC with high school science teachers, district-based coaches, and university researchers conducted collective inquiries over five years to improve science instruction. The PLC was situated in a culturally and linguistically diverse school that experienced high teacher and administrator turnover. This study aimed to explore 1) how the PLC developed multiple lines of inquiry to support students' scientific modeling over the first four years and 2) how five participant teachers' collaboration and classroom teaching to support students' construction of evidence-based explanations co-evolved during the last year of this study. This study was conducted as part of a larger research-practice partnership project. I joined the project in the third year and participated in the focal PLC as a participant observer. To explore how the PLC developed lines of inquiry over four years, I qualitatively analyzed video recordings of the participants' interactions on twelve job-embedded professional development (PD) days (about 96 hours) where the participants engaged in cycles of collective planning, teaching, and debriefing of lessons. I also analyzed artifacts and interview data. Data suggest that, despite the turnover, the participants developed three lines of inquiry to improve sets of instructional practices to support students' scientific modeling, specifically aimed at facilitating 1) students' epistemic work, 2) students' productive collaboration, and 3) students'--especially emergent bilinguals'--academic language learning. To explore how the teachers' collaboration and teaching co-evolved in the last year, I qualitatively analyzed the video/audio recordings of teachers' interactions on one job-embedded PD day and in eight after-school meetings (about 19 hours) as well as their classroom teaching (34 lessons). I also analyzed artifacts and interview data. Data suggest that the teachers' collaboration in the PLC and their work in classrooms co-evolved over time, as the teachers actively negotiated their goals and expectations about student learning, identified problems of practice, and developed and tested a suite of instructional practices for supporting students' construction of evidence-based explanations. This study suggests implications about how to study and support teachers' collective inquiry over time. [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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]