“What's the Big Idea?”: A qualitative analysis of the big ideas of primary science teachers

•Primary teachers’ Big Ideas afford unique insight into the discrepancy between research and classroom practice.•A priori and emergent analyses were conducted on the science Big Ideas of 40 teachers.•Participants’ general ideas about science were more developed than their ideas of science disciplines.•Teachers emphasised scientific literacy in ways that accord with current research.•Big Ideas can frame teacher reflection and development across educational contexts. Big Ideas are an emerging area of research that afford insight into how teachers conceptualise their practices. This research aims to investigate the science Big Ideas of a sample of 40 Australian primary teachers. Participants articulated their science Big Ideas through interviews and/or online surveys. An a priori qualitative analysis utilising Harlen's “Big Ideas about and of Science” was supplemented with emergent thematic analysis. Participants’ ideas about science (i.e. the nature of science) were considerably more developed than their ideas of science (i.e. science content knowledge). The teachers’ emphasis on scientific literacy aligns with current research.