Halliday & Matthiessen (1999: 617-8):
But there is a further transformation still to come, when experience is once again reconstrued, this time as technical knowledge. This reconstrual too is institutionalised, in the transition from primary to secondary education: when children move into secondary school, as adolescents, they learn to organise their experience according to the disciplines — mathematics, science (chemistry, physics, biology), geography, history, and so on.
Semiotically, the critical factor is that of metaphor; the semiotic bonds that had enabled the child to learn the mother tongue in the first place, bonds between figures and their elements on the one hand and clauses and their transitivity functions on the other, are systematically (and more or less ceremonially!) untied. The categories of experience are deconstrued, to be recategorised over the remaining years of schooling in the "objectifying" framework of grammatical metaphor. …
By the time children reach the 11th and 12th year of education their experience is being construed in terms such as these:
Every similarity transformation, if not a translation, reflection, rotation, or enlargement, is the product of two or more such transformations.What would be the order of magnitude of the moment of inertia of the Earth about its axis of rotation?
The elements are processes and qualities that have been metaphorically reconstrued to become participants: rotation, magnitude, enlargement, and so on; together with the relation of identity construed as a process by the verb be. When our adolescents' ideation base comes to accommodate a meaning potential of this technicalised kind, we consider that they have reached semiotic maturity.