ABSTRACT
This chapter describes the design and evaluation of an instrument to assess the topic specific pedagogical content knowledge (TSPCK) of a sample of Grade 12 teachers in organic chemistry. Organic chemistry has long been regarded as a difficult topic in the curriculum at both secondary and tertiary levels. It can be described as a linear sub-discipline of chemistry where comprehension of basic concepts is essential to build a secure knowledge base. The version of the instrument was administered to a sample of teachers from schools in South Africa. The Rasch model is built on the assumption of unidimensionality, which means that all items must work together to measure the same variable, namely, mastery of organic chemistry in the CK questionnaire and topic specific PCK for the PCK questionnaire. The Rasch analysis of the instrument provides guidelines on how the questionnaires and rubric could be refined for future use while at the same time allowing the data captured for the sample.
