Teachers and researchers alike have advocated over the last decade writing across the curriculum, which has tremendous potential both for improving the writing process and as a tool for helping students develop subject matter understandings. In particular, evidence shows that writing-to-learn has promise as a powerful tool for supporting students through a process of conceptual change in elementary school science; however, little research has been done in this area. Many researchers believe that social and instruction norms for school science and writing form early and are strongly held. Therefore, the teachers using writing-to-learn in science has a dual challenge: to change the existing norms of science learning from focusing on memorizing facts or doing "neat activities" to developing connections and understanding relationships among ideas and to change the norms for writing from knowledge telling, with the teacher taking on the role of evaluator, to using writing as a tool for puzzling over ideas and making connections. This paper shows how much change is possible in the course of one science unit, given the existing social and instruction norms of both teacher and students in a third-grade science class. It tells of the struggle the teacher went through in trying to use both oral and written discourse in new ways in order to promote student knowledge growth in science and the struggle that students went through as they were presented with the new way of thinking about science and writing. Included is a description of the teacher's gradual shift back to a more traditional way of teaching as she began to "fit" the ideas of conceptual change science teaching and writing-to-learn within her more familiar framework of exposing the students to ideas, finding out what they think, and telling them the scientific concept. Also included is an analysis of two students' writing in science and their perceptions of the ways in which this writing resembles or differs from other writing done in science across the year. (Author)