"You is well old now innit?" - David Thorpe

No, this wasn't something one of my kids just said to me - but the message on a 20th birthday card to my stepson last week...

It made me think of the challenge a groan-up writer has in making authentic the speech patterns of their teenage characters.

A Mancunian editor this month asked me to look again at the dialogue of one of my teen characters. I've re-read the dialogue and ok, there's always room for improvement, but my question is: what constitutes perceived authenticity?

Firstly, I know plenty of educated teenagers, like my characters, who speak fairly adult-like. They may also come out with "It was like awesome and totally mad" type idioms from time to time, but only when discussing certain things, usually geeky stuff.

They can easily switch to more adult diction when discussing serious topics. Not every kid talks like a south London wannabe rap artist.

What's more if you do any research online on how teenagers are supposed to talk you come across hilarious threads like this on mumsnet, where parents are striving to make sense of their youngsters' slang.

What this thread drives home is that this slang varies dramatically from one part of the country to another, almost reassuringly continuing to maintain regional differences.

What's more, much innovation comes from youngsters themselves experimenting creatively, coming up with either new words or different meanings for existing words. Their ears are hyper-tuned to naunces and new phrases uttered by their peers and by artists they listen to.

It's both a competitive process - being the first to latch onto a new trend - and a collaborative, peer group-gelling one.

I remember it well from my own teenage years. A few of these words go mainstream, many die out in a kind of Darwinian selection process.

The regional variations may explain part of the problem my Mancunian editor is having. So here in South Wales kids still use words like "crackin'" and "oober", but I have no idea what they say in Manchester.

Then again, there's the class angle, and it's more likely that working class (if I can use this term - I tend to avoid the c**v word) are going to use this type of slang than middle or upper class kids, who will speak more proper, like.

Moreover, my book is set 18 years into the future, and I can't possibly know how teenagers are going to be talking then, nor do I want to distract the reader by inventing new slang, which has been a recent trend in literature, triggered by Russell Hoban's Riddley Walker and taken to extremes by, say, David Mitchell in Cloud Atlas, that I consider has been a bit overdone by now.

Actually I think creating authentic teenspeak's got less to do with the slang words used and more to do with what thinking processes and abilities are revealed in speech.

Teenage boys in particular are not exactly renowned for being articulate and expressing or understanding emotions, are they? Then again, some are better than others.

They will reveal themselves by what they don't say as much as what they do say.

So I'm interested in other YA writers' approach to this problem. How do you go about making your characters seem convincing in speech?

Do you base them on existing people you know? Do you make up words? How do you avoid the problem of dating in language, or don't you care? Do you have young readers you test out dialogue on?