A longitudinal case study was conducted to explore changes in how beginning science teachers conceptualize science teaching. The current study explored the development of two of these teachers who were chosen because of their contrasting levels of expertise after their first semester of independent teaching. The research was designed to elicit the participants' personal beliefs about science teaching and science teachers. Three data collection methods, concept mapping, a repertory grid interview technique and stimulated recall interviews were used to allow triangulation. Data were collected as early as possible in the preservice year, at the end of that year and after one and three semesters of independent teaching. The initial stimulated recall interview for each participant occurred during the first continuous 3-week teaching experience. Findings raised questions about possible implications for selection, preservice education, and induction of science teachers to enhance the quality of the contribution of new members of the profession. Appendixes show the frequencies of comments in different categories in each stimulated recall interview, the focused forms of each repertory grid, and concept maps drawn at each stage. (Contains 26 references.) (LL)