Lisi Harrison's best-selling "Clique" series chronicles a group of bratty, fashion-obsessed seventh-graders who claw their way to Queen Bee status by trashing those unfortunate to be on the outside. So, the infectious giggle and sense of humor that punctuate a telephone interview with the author is unexpected.

Shouldn't someone who writes so knowingly about middle school Mean Girlhood be a Mean Girl herself?

Yet when congratulated on the 7 million copies of her books in print -- and counting -- the Canadian-born writer simply laughs.

"Why, thank you," she deadpans. "I printed them all myself!"

No one's more surprised by Harrison's success than Harrison herself. Despite a degree in creative writing from Emerson College in Boston, the whole "author" thing, where complete strangers read and enjoy your books, was too far out of even her imagination. And as the faithful can testify, the girl's got one heck of a vivid imagination.

"I had it in my dream plan but never thought it would be in my reality plan," says Harrison, who lives in Laguna Beach, Calif., but was calling from New York, where she was meeting with editors. "I couldn't fathom that."

It helped, of course, that when she published the first book in the series, "The Clique," in 2004, Harrison was senior director of development at MTV in Manhattan and knew producers, publishers and packagers along with people in development who were constantly pitching ideas for TV shows. (She created and developed reality shows such as "One Bad Trip" and "Room Raiders.")

When it occurred to her that the job was a lot like middle school -- so many of its adult employees would do and wear anything just to fit in -- she had the basis for a marketable idea.

"It was, 'Let's do a series on middle school and cliques,' " she recalls.

Instead, she put pen to paper. And, in the process, Harrison proved not only to have an ear for teen-speak, but also a handle on their angst, wants and desire to be accepted.

Her second book about main character Massie and her equally fab friends, "Best Friends for Never," reached The New York Times best-seller list four months after it was published in 2005.

The "Clique" series now counts 11 books, plus a five-book "summer" collection, and today the first book in a new spin-off series, "Alphas," arrives in bookstores. "The Clique" on Red Bull, it centers around an ancillary character, Skye, who attends an all-girl academy for Alpha girls on a private woman-made island. (Seriously.)

"I wanted to kick it up a notch," says Harrison, laughing.

There's also a "Cliquetionary" coming out in October (a Mean Girl calling you an LBR is not a compliment!), along with the prequel, "Charmed and Dangerous: The Rise of the Pretty Committee." So crazy is her schedule that ghostwriters may have to start working with Harrison on the series.

"Lisi was always very creative and focused and very driven," says Bob Kusbit, of One Louder Productions in the Strip District, who worked with her at MTV on the series "Made" and "Boiling Point."

Most people give up when one of their ideas fall flat. "But she would find a way to push it along and reshape it until people finally bought into it," says Kusbit, now head of development for MTV Networks' Country Music Television. "Her success doesn't surprise me."

With its irreverent tone, snappy dialogue and emphasis on shopping and physical appearances, Harrison's work -- aimed at 8- to 12-year-olds -- has been described as "chick-lit for tweens." Critics might take issue with the books' Mean Girl antics (the characters are as rude as they are stuck-up) and conspicuous consumption (it's a world dominated by Louis Vuitton backpacks, Prada skirts and Jimmy Choo stiletto sandals). But they're fun and entertaining and, like the Pinkberry smoothies the gang loves to guzzle, oh-so-addictive. In other words, they get kids reading.

Not to mention writing. Harrison said her garage is stuffed with boxes of glitter-covered letters from young female fans. She also gets countless e-mails through her Web site, www.lisiharrison.com. Responses come in the form of "shout outs" on her weekly blog.

"She's definitely popular," says Karen Brooks-Reese, coordinator of teen services at Carnegie Library of Pittsburgh, where Harrison's books are always on hold.

Tweens, she says, love reading about the rich and fabulous lifestyles they find so intriguing without having to move up to the next level of books that might not be age-appropriate.

"It's 'Gossip Girls' for middle schoolers," Brooks-Reese says, referring to the racy series of books for young adults that spawned the even racier TV series of the same name.

Is is great literature? Probably not. Does the series' message elevate tweens to a higher level morally? That's debatable.

But girls are obviously getting something out of it, says Brooks-Reese.

Some teens want their books to contain mirrors where they can see themselves, while others prefer a window, she explains. "These are books for kids who want a window into a different lifestyle."

Harrison readily acknowledges the books are over the top for a reason. Exaggerating her characters' obsession with fashion, she argues, shows how ridiculous it is -- a satirical point not lost on her readers. "The girls get it," she said, even if their parents don't.

At the same time, the mother of two daughters hopes to show readers that Mean Girls are mean for a reason, and that even the nastiest girl can grow as a person over time. Ringleader Massie might appear to have her life together, but she's horribly insecure, says Harrison, tossing and turning at night in her struggle to stay on top. "It sort of deconstructs the bully for a lot of girls."

What she hopes girls take away from both series is that we're all complex and a little bit of a mess, and it's the rare soul who hasn't done something really crazy to fit in. Harrison also wants them to realize, in a big-picture way, that middle school is just one period in their lives.

"They need to widen their lens and understand this is just the first act of many."

Presenting the issues and pressures and horrors of cliques through satire and fantasy wish fulfillment makes them more acceptable to girls.

"It makes them funny," says Harrison.