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An educational approach in which students perform experiments that demonstrate explicitly the reversibility of chemical reactions and the possibility that chemical reactions do not go to completion has been developed. Little attention has been given to changing students conceptions of chemical reactions as a result of the introduction of the chemical equilibrium concept. There is evidence that students do not understand the dynamic nature of chemical equilibria.

In this position paper, we examine the science teaching orientation component of the S. Magnusson, J. Krajcik, and H. Borko (1999) pedagogical content knowledge (PCK) model for science teaching. We trace the origin of the construct in the literature, identifying multiple definitions that have lead to ambiguity. After examining published studies using the PCK model, we identified the following methodological issues: (a) using orientations in different or unclear ways, (b) unclear or absent relationship between orientations and the other model components, (c) simply assigning teachers to one of nine categories of orientations, and (d) ignoring the overarching orientation component. To bring clarity to the literature, we propose defining science teaching orientations as a set of beliefs with the following dimensions: goals and purposes of science teaching, views of science, and beliefs about science teaching and learning. Consequently, there is a need for new instruments to elicit these dimensions. We conclude by making recommendations to address the four issues identified in the literature. [ABSTRACT FROM AUTHOR]

This study investigated the knowledge that experienced science teachers have of models and modelling in science in the context of a school curriculum innovation project in which the role and the nature of models and modelling in science are emphasized. The subjects in this study were teachers of biology, chemistry and physics preparing for the curriculum innovation. Two instruments were used: a questionnaire with seven open items on models and modelling, which was completed by 15 teachers, and a questionnaire consisting of 32 items on a Likert-type scale (n=71). Results indicated that the teachers shared the same general definition of models. However, the teachers' content knowledge of models and modelling proved to be limited and diverse. A group of teachers who displayed more pronounced knowledge appeared to have integrated elements of both a positivist and a social constructivist epistemological orientation in their practical knowledge. Implications for the design of teacher education interventions are discussed. [ABSTRACT FROM AUTHOR]