As a result of the Biological Sciences Curriculum Study (BSCS), instructional content and style were studied in six teachers teaching the concept of photosynthesis. The same BSCS curriculum program was used by all six teachers; all six had some previous BSCS training. The students in the six classes had been selected on the basis of high ability and/or high achievement. Three consecutive class sessions were recorded during the introduction of photosynthesis and analyzed by the topic classification system of Aschner, Gallagher, and others. Significant interteacher variations were found on dimensions on teacher intent and level of conceptualization but not on teacher style. Wide variations were found among emphases on various biological concepts or background materials. It was thus concluded that using the same curriculum materials does not insure similar instruction. (Author/JD)