This study examined changes in the science content representations of two prospective elementary teachers during their first year in an experimental teacher preparation program. Qualitative case study design guided data collection, organization, and analysis. Multiple farms of data, including audio-taped interviews, written documents, and videotaped teaching episodes, were collected across two complete cycles of planning, teaching. and reflection. Data on prospective teachers' content representations were analyzed for their accuracy, sequencing, and connectedness, as well as their attention to the needs of learners. improvements in content representations were noted within each component of the cycles and across semesters. These changes appear to be closely related to prospective teachers' developing understanding of learners. Findings suggest that opportunities to engage in cycles of instruction guided by structured considerations for content representation contributed to the noted improvements. (C) 2000 John Wiley & Sons, Inc.