So, what is it? Far be it from us to pontificate, but we do know what the research community means by it, and we think this is also what the national curriculum means. All its examples involve non-standard forms such as "they was". Look on page 23 of the English document and you'll find a list of other examples: "have fell", "I done", "ain't", "come quick" and "them books".
What these forms have in common is that you won't find them in books (except of course books about grammar - or books with deliberately non-standard dialogue). Nor will you find them in The TES (except for special effects). Standard English is the English of publishers, and a remarkable achievement it is too: more or less uniform the world over. For all you know, we could be Americans or New Zealanders - you couldn't tell from our English. Yes, there are differences between American and British English, but they're tiny and you could read pages of a book before you found a give-away word.
So standard English is international English. (Notice that we're not saying anything at all about pronunciation - of course that's not at all international. We're just talking about grammar.) Some see it as an example of global imperialism, but equally you can see it as our gift to the world.
And what a gift to all our pupils, many of whom learn it as native speakers. Well, not quite native speakers. What makes standard English sensitive in our classrooms is that most pupils' native English is slightly different from standard English. We don't know the figures for sure, but probably around 90 per cent speak non-standard at home and have to learn standard at school.
Unfortunately this gives the privileged few a head start; but not a very big one because the differences are pretty trivial.
If pupils ask you what standard English is, the answer is simple: it's what they find in books and what they hear from your lips.
It doesn't have to be very formal - for example, it doesn't force you to write "does not" - we've just written "doesn't", and there it is, in The TES. Nor does it have to have a posh accent. In short, it's the language of education - and that's why they need to know it.
Richard Hudson is professor of linguistics at University College, London Geoff Barton is headteacher of King Edward VI School, Bury St Edmunds, Suffolk