Describing and analyzing teaching practice has been a focus of researchers interested in the interaction and connections between teachers' content knowledge and their pedagogical knowledge. This study described the role of a teacher's mathematical content and pedagogical content knowledge in involving students in learning and solving Science, Technology, Engineering, and Mathematics (STEM) problems in an Australian primary school context. The Knowledge Quartet (KQ) is a widely recognised framework originally developed to observe classroom mathematics teaching and analyze mathematics teaching practices. We use the KQ as a theoretical/organizational framework against which to thematically analyze one teacher's classroom pedagogy to investigate 1) the utility of the KQ framework for describing and analyzing a teacher's mathematical lesson within an integrated STEM inquiry context and 2) how a teacher's pedagogical mathematical knowledge supports a focus on inquiry-based STEM integrated teaching. The study involved a teacher and 26 Year 5 students in an Australian classroom. Data included classroom video recordings, researcher observation notes, and students' artefacts. The video recordings were transcribed and analyzed using the KQ framework. The observation notes and artefacts were used to validate and support this analysis. The paper identifies and provides examples of different aspects of the KQ in the teaching sequence and provides examples of how integrated STEM content can be effectively incorporated into the primary school classroom. The relevance and significance of the KQ framework and the teaching of integrated STEM content in primary school are reviewed and discussed within the paper.