The appropriation and appropriate use of the language of school science is a widely acknowledged goal of science education (Lemke, 1990; Mortimer and Scott, 2000; Sutton, 1996; Wellington and Osborne, 2001). This study examines how students appropriate and employ the language of school science in the context of a science classroom. For the purpose of this study, the data analysed are the lesson transcripts and students’ written assignments generated from a sequence of lessons on the topic of “States of Matter”. By employing analytical categories from the Systemic Functional Linguistics framework (Halliday, 1994), we analysed the students’ written language and compared it with the language used in the whole-class instruction. Several differences in the use of certain linguistic resources were identified that highlight the challenges that students face when appropriating the language of school science. The significance of these differences is illuminated by considering the notion of ‘condition-of-use’, which refers to the circumstance under which a particular linguistic resource is used. Our findings suggest that the condition-of-use of linguistic resources is a significant aspect of the language of school science that needs to be appropriated by students if they are to employ the language of school science effectively.