The intervention programmes have a direct influence on teachers' knowledge of teaching different topics. This paper focuses on how Grade 8 natural science teachers' knowledge developed during an intervention programme. Eight schools were selected to participate, and 25 Grade 8 Natural Sciences teachers from Gauteng province participated. Data were collected during the intervention sessions, and participants completed a written TSPCK test and content representation tool. Quantitative data were analysed using the Rasch analysis model, and qualitative data were analysed using content analysis of TSPCK episodes using the TSPCK rubric. The episode was a response segment, where TSPCK components were used to transform the topic content. The findings showed that teachers' pedagogical content knowledge improved significantly in different components of TSPCK. The teachers' PCK development was revealed through extensive use of knowledge of representation including demonstrations using diagrams aimed at transforming the concept in planning. Besides, during the intervention, teachers were able to collaborate, have explicit discussions on specific topics, and provide explanations on the use of the five TSPCK components. The study implies that the development of PCK in fundamental topics in a discipline can be implemented through a TSPCK-based intervention.