Constructivism in science education has been the subject of considerable debate in the science education literature. The purpose of this study was to facilitate chemistry teachers' understanding that the tentative nature of scientific knowledge leads to the coexistence and rivalries among different forms of constructivism in science education. The study is based on 17 in-service teachers who had registered for a 11-week course on "Epistemology of Science Teaching" as part of their Master's degree program. The course is based on 17 readings drawing on nature of science and a critical evaluation of constructivism. Course activities included written reports, classroom discussions based on participants' presentations and written exams. Based on the results obtained, it is plausible to suggest that participant teachers experienced the following transitions leading to greater understanding, as they acquired experience with respect to constructivism: (a) Active participation of students as a pre-requisite for change; (b) Different forms of constructivism represent competing and conflicting interpretations of progress in science; (c) Acceptance of the present state of constructivism as a Kuhnian paradigm; (d) Social constructivism as the preferred form of constructivism; (e) Critical appraisal of social constructivism; (f) Despite its popularity, social constructivism does not constitute a Kuhnian paradigm (due to controversies, there is no consensus in the science education community); (g) Contradictions faced by constructivism in science education provide the base for its advance and evolution towards more progressive forms, and hence the need to consider, whither constructivism?