"An effective National Curriculum therefore gives teachers ... understanding ...at school. It allows schools to meet the individual learning needs of pupils and to ...local communities. And it provides a framework within which all partners in education can support young people on the road to further learning."
We rest our case.
And yet we all know that words like and are co-ordinating conjunctions (words used to link clauses within a sentence). If so, the words on either side of and must be part of the same sentence, so they shouldn't be separated by sentence punctuation.
What's going on? And more importantly, what should you tell your students? The fact is that punctuation has two different jobs.
The basic job is to signal grammar, which is where key stage 2 children start. A full stop shows a gap in the grammar - no grammatical link.
Seven-year-olds may write like this: Once upon a time there was a coloured egg I put it in a nest and one day it went crack ...
But here a full stop is definitely needed after egg to signal the absence of any grammatical link to the next word - in other words, a sentence boundary.
Their other job is to chop up the text into manageable chunks of information, even if this means putting "sentence punctuation" in the middle of a sentence. This is why the National Curriculum example works so well.
Sometimes the effect of a full stop before and is to emphasise this word; separating the clauses with a full stop allows us to draw attention to (or "foregound") that link. And that's where we move awayfrom pure issues of grammar into matters of style.
Good writers make informed decisions about language, and break the elementary "rules" where necessary. But such language use needs to be informed. And not gratuitous.
Richard Hudson is professor of linguistics at University College, London Geoff Barton is headteacher of King Edward VI School, Bury St Edmunds, Suffolk