Examination of existing science curricula and school science practices reveals that scientific argumentation, among other approaches, in teaching science is effective for developing students' scientific enquiry and reasoning. However, much research has shown that science teachers have struggled to integrate it into science learning and teaching. This thesis explores science teachers' pedagogical development of scientific argumentation through sustained collaborative work and reflection. The study adopted an embedded case study approach and involved the generation of qualitative data from three science teachers working in a comprehensive school in London (through lesson planning, lesson observations, reflective interviews, and students' written work). This thesis also utilised the concept of agency to examine teachers’ pedagogical development. The comparative analysis of teachers' practice showed that their initial approach to implementing scientific argumentation evolved, with variations according to teachers’ characteristics, values and emphasis on teaching science, approaches and scaffolding scientific argumentation processes, timing and the organisation of their students for discussions. Reflection on practice and collaborative work with colleagues helped them construct a better understanding of scientific argumentation and its value for learning science. Additionally, the variations in students' written work provided insight into the differences in their teachers' scientific argumentation approach. The results indicate the need for better support for teachers in planning and incorporating scientific argumentation into their practice through more focused professional learning. Additionally, this study examined changes in teachers' pedagogical development through the lens of agency, specifically in the components of sense of purpose, mastery, autonomy to act, and reflexivity, and identified factors that seemed to support or hinder the development of agency. The findings of this thesis contribute to a better understanding of how scientific argumentation is incorporated into teaching science and how the concept of agency may be useful to examine teachers' pedagogical development of new teaching approaches
