Promoting relevant, meaningful, and equitable science teaching learning environments for both teachers and students has become a critical objective for science education. To achieve this goal, fostering students' sensemaking experiences in science becomes critical. Working towards such a committed, and equitable sensemaking environment is closely connected to the developing identity trajectory of the science teachers. Teachers prioritize certain conceptions, beliefs, and practices in their science classrooms based on their "personal prior experiences," conceptions of science teaching and learning within the larger parts of their institutional system, and instructional choices, and eventually practices in teaching science. These practices and conceptions connect back to their ever changing historical, social, and cultural backgrounds and experiences; their interactions and relationships with their communities and institutions; and therefore, to their teacher identities. Over the past decades, there has been robust research regarding teachers' identities, perceptions, and conceptions of teaching science. In addition, most research on science teacher identity has been on personal histories of teachers and how they shape and reveal certain science identities. This emphasis on personal stories reflects on individualistic view on science teacher identity and crafted by mainly utilizing data sources such as written or oral reflections and teacher interviews. Therefore, several scholars claimed that more research on the nature and characteristics of the contexts and systems are needed to understand the ways that identity is influenced by multiple histories of participation. Considering there is still much to learn about how we can capture and interpret the meaning behind science teacher identity to make critical implications on teacher development and student sensemaking in science, this study has two main aims a) investigating the relationship (interaction) between teacher's changing practice and students' sensemaking experiences in learning and doing science, b) investigating an elementary teacher's developing identity to teach science considering her personal history and changing conceptions and practices on science teaching over years. To do so, I conducted a single case study using longitudinal qualitative research (LQR). I specifically zoomed in on Ms. Spark's use of sensemaking practices while teaching 3rd grade science. Data sources include detailed observation field notes, individual interviews with Ms. Spark, and student work and artifacts over three years (between 2018 and 2023). The findings present the journey of an experienced teacher, Ms. Spark, as she keeps developing a reform-based mindset in teaching elementary science using PBL-oriented curriculum materials and sensemaking practices. This study has important implications for teacher education, professional development, curriculum, and instruction. The evidence indicates that sensemaking practices can be used as a tool and support for pre-service and in-service elementary teachers as they learn to teach science in a sensemaking, equity, and justice-oriented vision. The sensemaking practices provided a mindset and set of pedagogical guidelines for the teachers where they can leverage equity and justice-oriented, humanizing approaches to science teaching in defining, redefining, and implementing their teaching practices. In addition, this research contributes to our understanding of how a teacher's personal background and positionality, as well as their experiences with other collective and systemic structures (besides the university methods course), such as their current and future relationships with their field placements, school administrations, district leaders, curriculum coordinators, research partners, or their colleagues could help researchers to capture the complexity of developing teacher identity. [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.]