Chapter 10 The impact of a professional development intervention on Physical Science teachers’ conceptual change W.T.Dudu Abstract Changes in classroom practices demanded by reform visions such as the shift from the National Curriculum Statement (NCS) to Curriculum and Assessment Policy Statements (CAPS) ultimately rely on teachers. A great deal of learning on the part of teachers is required if changes of this magnitude are to be a success. Teachers − just like their learners − also harbour alternative frameworks in Chemistry concepts. Studies show that teachers reflect these alternative frameworks in Chemistry classes, especially when abstract concepts are being taught. The purpose of this study was to examine the impact of a support and guidance professional development intervention program in practical work on Physical Science teachers concerning various Chemistry aspects. The study was guided by the conceptual change theoretical framework. A case study research method was used in the survey. The sample consisted of 123 Physical Science teachers and 7 Physical Science subject advisers drawn from the North-West Province of South Africa. The data was collected while teachers performed the actual prescribed and recommended Chemistry practical activities suggested by the CAPS document. Data was analysed using criteria adopted from Muchtar (2012). The results indicated that teachers harbour alternative frameworks in various Chemistry concepts. Findings showed that basic concepts about electrochemical cells, reaction rates and acid- base titrations were hardly understood by some of the teachers who participated in this study, though all have taught Chemistry as a component of Physical Science in their classes for years. To a larger extent, the professional development intervention had an impact on the teachers and their performance improved after the intervention. The significance of this chapter rests in recommending more such interventions throughout the year which enables teachers to improve in their content knowledge