This Australian Research Council study investigates the pedagogical reasoning of expert teachers of science in the planning phase of their work in an attempt to explicate the usually tacit thinking underpinning teacher practice. Our framework includes four foci that emerged from a precursor study: big ideas; quality learning, student engagement and contextual constraints. Over the 2 years prior to this event, the research team have worked with 40 primary and secondary teachers to explore the degree to which these foci map onto their practices as they plan a unit of work for their respective students. Findings to date indicate that these four foci (with a fifth focus emerging from the current teacher cohort) resonate with teachers giving them a shared language along with ways in which to more clearly articulate the thinking behind their planning and implementation with colleagues, students, and other educational stakeholders. In this seminar, we provide an overview of the research while highlighting a number of key findings around teacher pedagogical reasoning.