| Summary: | Includes bibliographical references. === The prominence of practical work in science curricula today infers that these activities offer unique learning experiences for achieving specific goals. Yet, but for a few exceptions, practical work in school science is often neglected and has not been effective in achieving the goals normally associated with it. The rationale behind this study was that an understanding of the bases for decisions made as teachers plan, enact and assess practical work in Grade 8 and 9 natural sciences, may reveal the nature of the knowledge base required for effective practical work. It was thought that such insight might also shed light on some of the reasons for the apparent lack of effective practical work in South African schools. Furthermore it could inform the design of those aspects of pre - service and in - service teacher professional learning programmes aimed at developing the knowledge and skills required for effective practical work. There is a paucity of research on the knowledge base required for science practical work and no instruments designed to measure, capture or describe such a knowledge base, were found. The aim of this study was firstly to develop a valid and reliable instrument to facilitate the analysis of what teacher s say and do with respect to practical work, and secondly to get a feel for using this instrument for the purpose it was intended. Informed by literature, and using Shulman’s notion of pedagogical content knowledge (PCK) as the theoretical lens, the analytical instrument, called the practical work PCK table (PPCK T able), consisting of different categories and sub - categories of knowledge, was developed. A number of strategies were used to improve the validity and reliability of the instrument. These strategies included: i) using the instrument to analyse interviews and lessons of three natural sciences teachers working in three different educational settings, ii) soliciting the input from experts in the field of PCK, and iii) determining the inter - rater agreement in the interpretation of the categories or sub - categories among four raters by calculating the percentage agreement and the Fleiss’ kappa statistic. Addressing the shortcomings revealed by these measures culminated in the final version of the instrument, the practical work knowledge table (PracK Table) and its accompanying codebook. The second aim was addressed by conducting a pilot case study to explore the usefulness of the PracK Table as a heuristic device. A series of eight Grade 9 lessons taught by one teacher were observed. Data sources included lesson observations, teacher and learner interviews, worksheets and samples of learners’ work. The PracK Table was used to identify and describe the knowledge the teacher drew on when he engaged his learners in practical work. This study has shown the construct, ‘PCK for practical work’, to be invalid. It also revealed that a useful, valid and reliable instrument could be developed, if it is informed by authoritative literature, and if its validity and reliability are empirically tested in real contexts. In the case study the strengths and weaknesses in a teacher’s knowledge and practice could readily be identified using PracK Table as the analytical tool. The findings of the case study indicate that a broad knowledge base and access to laboratory resources, although necessary, does not always translate into effective practical work. Furthermore, it suggests that for well - qualified, experienced natural sciences teachers, teaching in fairly well - resourced schools, it is their theories about teaching and learning in general that is the main factor that determines the effectiveness of the practical work they engage in. These findings could have significant implications for the development of teacher professional learning programmes.
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