As Christie (1998) has emphasized, literacy learning is a continual process that spans the years of schooling, with "significant milestones… if students are to emerge with a reasonable degree of proficiency…. There is a relationship between the changing patterns of written language that students need to recognize and use, and the variety of knowledge they need to learn" (pp. 49-50). It is this latter link that is crucial, and there are parallels to draw with mathematics as I shall show. Using Systemic Functional Linguistics (Halliday,1994), Christie maps the development of writing from early "and then" recount, which is based on personal experience and is closer to speech than to “mature” writing, through a middle years explanatory or procedural mode which shows command of tense, technical and explanatory language and an authoritative author role, to later years expository or argument-based writing, which is marked by control of grammatical metaphor and the removal of agency.