Knowledge and semiotics are inseparable. From a perspective of systemic functional linguistics, knowledge is created, developed and realised through semiotic resources, among which language is a critical one. As far as language is concerned, the process of developing knowledge is at the same time the process of developing the language of that knowledge. The initial linguistic development of knowledge starts from children’s birth and there is ‘continuity between home, neighbourhood and schools as environments for learning’ (Halliday, 1990/2007, p. 360). According to Halliday (1998/2004), there are three crucial changes throughout this developmental trajectory—including the move from protolanguage (Halliday, 1975/2003; Painter, 1984) to language in the second year of life when children start to develop grammar (Painter, 1999); the move from everyday spoken language to written language when they enter into school around age 5; and the move from written language to the language of subject disciplines when they enter into secondary school (Halliday, 1998/2004, p. 27). These critical moments can be rephrased as the moves into ‘commonsense knowledge’ (age 1–2), into ‘educational knowledge’ (age 4–6) and into ‘technical knowledge’ (age 9–13).