This study is concerned with the impact of an intervention on the development of the pedagogical content knowledge (PCK) of pre-service teachers in the topic of electromagnetism, during a physics methodology module. The study is guided by the following question: How is the development of the PCK of pre-service teachers influenced by the explicit inclusion of topic specific PCK about electromagnetism in pre-service teacher education? Explicit instruction about the components of TSPCK as applied to the teaching of electromagnetism was employed as part of the intervention. This qualitative case study, conducted in two phases, was supported by quantitative analysis using the Rasch model. The first phase, involving 14 final-year education students specialising in teaching Physical Sciences, investigated the impact of the intervention, which was determined through pre- and post-assessments using diagnostic questions for content knowledge (CK) and a CoRe tool for PCK. By racking the data in Rasch analysis, the perceived difficulty of items in the CK-tests and CoRe tool could be established and this enabled the researcher to report on specific areas of difficulty in electromagnetism that students encountered both in terms of their own conceptual understanding and in teaching of the topic. The study showed a significant improvement in the CK and PCK of the participants and revealed that the impact on curricular saliency and representations was more pronounced than on the other components. Students’ persisting inability to identify learners’ misconceptions and difficult concepts, was noticeable. In the second phase of the study, three students were observed and video recorded while teaching electromagnetism. The researcher established the extent of students’ enactment of the knowledge attained during the intervention and their pedagogical reasoning about their teaching. The study indicated that students were able to enact their PCK to teach towards conceptual understanding integrating the components skilfully, when teaching concepts with which they were comfortable. However, when teaching concepts where their own CK was lacking, their conceptual teaching strategies collapsed. During their first attempts to teach the topic, students did not follow a teaching sequence that lead to conceptual development of ideas, but they were able to adjust the sequencing as a result of this experience.