Pedagogical content knowledge is considered a valuable knowledge base for all science teachers. Thus, promoting its development in all pre-service teacher programmes including a short 1 year Physical Science postgraduate certificate in education (PGCE) course is desirable. This paper focuses on the comparison of topic-specific pedagogical content knowledge (TSPCK) at a level of planning to teach between PGCE pre-service teachers (n = 8) and final (fourth) year traditional BEd pre-service teachers (n = 16). Both groups were exposed to an intervention targeting the development of TSPCK in Physical Science topics taught in South Africa's national secondary school curriculum. Data collected from both groups comprised pre-post intervention TSPCK tests and content representations tool for chemical equilibrium. The data analysis entailed the use of a criterion-based rubric for shifts in the quality of planned TSPCK and the content representations were analysed through an in-depth qualitative analysis. The findings revealed an improvement in the PGCE pre-service teachers' planned TSPCK to the same extent as for the BEd pre-service teachers. The PGCE pre-service teachers did not indicate being at an initial advantage in their TSPCK because of their strong content knowledge, but they showed a faster growth path in developing TSPCK. Recommendations made include the promotion of TSPCK discussion in the PGCE programme and a possible re-positioning of such discussions in the BEd programme.