This case study is part of a larger study of teachers' use of curriculum materials in planning and teaching fifth-grade science. This case study focuses on one of the nine teachers observed teaching an activity-based unit on plant growth and photosynthesis. Although the teacher became aware that her students held certain misconceptions about plant growth, she was unsuccessful in helping them replace their misconceptions with the scientific conceptions she wanted them to learn. The analysis revealed several factors that contributed to this disappointing result. The teacher and the curriculum developers held different views about learning and the nature of science, and several problems surfaced about the content and organization of the teacher's guide.