For example, subjects such as geography and science push children to think through relations between things that co-vary - between latitude and temperature, or between height and weight - a really complex area of thought.
Quite often students' thinking is being pushed ahead of their grammatical abilities. So just how do you put a correlation into words?
Of course one reasonable answer is that you shouldn't try, that the best way to show a correlation is by drawing a graph. This is perfectly true as far as it goes, but it doesn't go far enough. Sooner or later the graph has to be translated into language, and that means grammar.
What are the grammatical options for describing a simple correlation between height and weight? The list is quite short if we're quite strict.
The best option is what grammarians call the Correlative Comparative, which consists of two comparative adjectives (or adverbs), each modified by the word the:
The taller people are, the heavier they are.
This construction is purpose-built for correlations, allowing us to express the generalisation that lies within them. It's the perfect solution. But how many key stage 3 children know it and use it? They probably know sayings like The sooner, the better and The bigger you are, the harder you fall and The more, the merrier, but that's not the same as being able to use the pattern easily in new sentences. So how does a teacher encourage this construction to grow?
By explicitly teaching it. A geography or science teacher has a duty to help students not only to master the concepts, but also to grasp the language with which to express their thinking. This is the heart of literacy across the curriculum with teachers saying things like: "Here's a useful construction which will help you to show that you understand today's topic. Let's make up some more examples. Those are all the more... the more sentences. What does this one mean? Can anyone draw a graph for this one? How do you translate this graph into a the more ... the more sentence?"
It doesn't much matter whether we tell students that they're using the Correlative Comparative (though in our experience, they like to know the technical terms).
What does matter is that we're giving students a language to express their developing understanding of the world - by explicitly teaching not only the geography and science concepts, but also the language structures they need to demonstrate their knowledge.
Richard Hudson is professor of linguistics at University College, London
Geoff Barton is headteacher of King Edward VI School, Bury St Edmunds, Suffolk