| Pedagogical content knowledge (PCK) has been described as an assemblage of the most powerful analogies, demonstrations, examples and illustrations that make content knowledge understandable to students, together with an understanding of the preconceptions and alternate conceptions that students bring with them to the classroom (Shulman, 1986). In speaking of representations, Johnstone (1991) and Gabel (1993, 1998) suggest that there are three categories of representations in chemistry: the macroscopic, particulate, and symbolic. For the present study, a fourth category has been added, the graphic representation. In addition, Bell, Veal & Tippins (1998) proposed a hierarchy of PCK, a structure wherein the broadest concept (science PCK) is specified by discipline PCK (chemistry PCK) and finally by topic PCK (Gas Law PCK). The present study will investigate the apex of this hierarchy, the intersection of PCK and the specific topic of the Gas Laws. The Gas Law PCK Model was created to illustrate the intersection of subject matter knowledge for teaching and topic-specific PCK. Four chemistry teachers, each holding a degree in chemistry, who had taught high school chemistry for at least three years, and who had taught the Gas Laws during each of the last three years, were given an assessment of their subject matter knowledge for teaching regarding the Gas Laws. Two interviews were conducted to address Gas Law PCK, focusing on representations and student preconceptions and alternate conceptions. Findings of this multiple case study indicate that the participants' subject matter knowledge for teaching, ability to move among representations, i.e. representational competence, and understanding of student alternate conceptions regarding the Gas Laws and how to address those conceptions were limited. Possible influential factors of curricula and lesson planning were also explored. Recommendations for emphasis on specific subject matter knowledge for teaching representations, representational competence, students' alternate conceptions and how to address student alternate conceptions were explored for pre-service teachers and in-service teachers. |
