Full-time teen, part-time author

So what did you do in your free time when you were 12? Play football? Torture your siblings? Obsess about boy/girl bands? Have slumber parties? Or does it all merge into one big collective memory of sweet-eating and furtive smokes, boredom, ever-changing gangs of friends and fads, and the seesaw transition from primary to secondary where you can't quite remember what it was you spent all that time doing, but it was grand all the same, thanks a million?

When Dublin-born Claire Hennessy was 12, she wrote a book in her free time. Let me run that by you again, folks. Dear Diary, the account of five months in the lives of five girlfriends, all 12, and written in diary form, will be published by Poolbeg on February 1st. Eason's has chosen it as its Children's Book of the Month. And that's not all: Poolbeg contracted her for a three-book deal when it signed her up. She has already written the second one and is about to start the third. And, incidentally, she hates English.

Claire Hennessy is now 13, and in her second year at Loreto High School in Beaufort, Rathfarnham. At her home in Dublin, she comes into the hallway to say hello; tall and slim and self-possessed, although initially so shy it's hard to hear what she's saying. That passes. She sits into the living room armchair, in the teenage uniform of jeans and trainers, her nails painted green and pink alternately, and relaxes.

"I've been writing stories since I was about eight or nine. We have a computer here at home, so I was used to messing around on it. The idea for the book came out of a story." She is quite definite that she would never have written the book if she hadn't been able to use a computer, because of all the hassle of rewrites, which in itself is something to meditate on. Maybe Claire Hennessy is the first of a whole new wave of very young writers, whose computer literacy will encourage them to be more ambitious about the story-writing that many children engage in at some stage of childhood, but which many lose somewhere along the way.

Did her family know what she was doing? "They knew I was writing something, but I've always been messing round, writing stories." Her friends didn't know either. "When I was finished, I thought there was enough for a book in it. And I sent it to Poolbeg because a lot of the books I'd been reading (Patricia Scanlan, Marian Keyes) were published by them." When she got the letter back from Poolbeg stating they wanted to publish the book, only then did she break the news to her astounded parents.

That was close on 18 months ago, and she only told her "best friends" about it the day before this reporter arrived to talk to her. "I thought they would all think I was weird and boring. Besides, I didn't think any of them would be interested," she explains patiently. "I didn't want them thinking that all I did was lock myself in a room and write. My life isn't like that."

When she finally told a couple of her best friends (just before the books were due to appear in the shops), the next day, the whole school knew by way of the grapevine. Presumably, jaws dropped collectively all the way from classroom to staff-room.

"It was chaotic," she admits cheerfully. "But I'm fed up with answering the same questions already. It's very annoying." One thing is quite clear: for a 13-year-old girl to keep such a meaty secret from her schoolmates for such a long time indicates admirable resources of character. If someone out there is looking for new Children of Fatima, to whom secrets can be entrusted, Claire Hennessy is definitely your woman.

The book itself is a simple, effective idea: five perspectives on the same events. The five friends, Aisling, Alison, Amy, Kate, and Megan, write diaries from February through to the end of June, about their friendships with each other, their stint in a Donegal Gaeltacht, school, boys, stepparents, birthday parties, the end of primary school. "It's a very girlie book," Claire says. "I hope girls from 11 to about 14 will like it."

It's a fair guess that a few mammies and daddies will be keen to read this book, to try to recapture some insights on the workings of a pre-teen mind, written straight from the horse's mouth. It's all pretty innocent stuff. Amy's diary says at one stage: "I took the Pledge at my Retreat last month. I said I wouldn't drink until I was 18. Still, I can see myself drinking alcohol before I'm 18. I just can't see myself taking drugs, because I swear, I'll never take anything like that."

Claire looks across the room suspiciously when this is quoted. "I do kind of agree with Amy, because a lot of people do break their Pledges, don't they? You're not going to write that I'm an alcoholic or anything like that, are you?" she says wildly: an early distrust of the dastardly ways of the media evident already.

At the beginning of each diary extract, there is a "Fact File" on each girl: Favourite actor, singer, film etc. Leonardo DiCaprio and Celine Dion feature a lot. So what about Claire's own personal "Fact File"? Who is her favourite actor? She twists her hands and says she doesn't have one, not really. So it isn't Leonardo DiCaprio then? She looks about as appalled as it is possible for a 13-year-old to look. The way a 13-year-old might look at a relative who turned up for the school play wearing something ghastly and uncool.

"No, no, no!" she declares. "Titanic was out when I was writing the book and everyone in Sixth Class was obsessed with Leonardo DiCaprio, they were all in love with him for about three months. Now if you say you like Leonardo DiCaprio, you're a social outcast. He's so Sixth Class."

She eventually concedes to liking Matthew Perry, who plays Chandler in Friends. Celine Dion is still her preferred chanteuse, and boy band Five and The Corrs are her favourite bands. Her favourite subjects are Maths and Business Studies, and she hasn't a clue what she wants to do later on. Be a full-time writer? She pulls a face. "Naw. I wouldn't want it as a full time job. This way, it's easier, it's my hobby, something I do in my spare time."

Poolbeg has signed her for a three-book deal, so we can expect one a year now for the next couple of years. "The second book is about two sisters fighting over a guy. The third one will be kind of a sequel." And when she gets her next advance, there's nothing she really wants to buy - except an inflatable armchair. No young writer should be without one.

Dear Diary, by Claire Hennessy, is published by Poolbeg for Children, at £3.99