This paper discusses linguistics in the teaching of science, specifically the key linguistic processes through which students learn, rather than the mechanics of classroom interaction. Integrated datasets from The Classroom Learning Project contain transcripts of videotaped lessons spliced with teacher and student interviews and annotated with a researcher's comments. To illustrate the role of language in determining the effectiveness of teaching and learning, an integrated data set for one Australian Year 9 (14 year old students) science lesson on 'Fibres and Fabrics' was analysed in terms of coherence and comprehension. The analysis demonstrates the importance of communication skills in the classroom and the value of language analysis in determining the effectiveness of teacher's instructions. This paper argues the need for teachers to consider the importance of learning as a linguistic milieu especially when teaching science in context. When teaching and learning in contextually, competent communication must include adequate, genuine, clear and relevant amounts of information.