This paper reports on four participants' perceptions of an interdisciplinary in-service programme incorporating science and English theoretical frameworks conducted with junior secondary science leachers over six months of teaching. The project aimed to examine the effects on teachers and students of the diversification of the uses of writing for learning in their classrooms. The programme focused on pragmatic issues such as specific strategies to increase opportunities for students to use writing to clarify and deepen their thinking, criteria for evaluating student writing, and effective uses of past student writing to clarify task demands. The paper focuses primarily on the effects on leachers' sense of their roles in teaching, their sense of science as a subject, and their perceptions of the effects on student attitudes towards, and knowledge of, science as a result of the in-service programme.