It was the sock that did it -- the sock that played music and had an embroidered Santa Claus.

Erinn Johnson-Long's other sock did not even match, which might have been a good thing because one piece of musical holiday footwear seemed more than enough. The 17-year-old senior at Montgomery Blair High School sat in the hot seat on the TV makeover show "What Not to Wear" and tried to explain her fashion choice.

"Why do you have to wear matching socks?" she asked the show's style gurus. The impeccably dressed hosts, Stacy London and Clinton Kelly, stared at her. Fashion rule number one, they said: Your socks have to match.

So began Johnson-Long's week-long lesson in personal style, documented in a back-to-school episode of the show scheduled to air tonight on TLC. The episode follows Johnson-Long's attempts to layer clothing, choose complementary colors and boost her fashion confidence with the help of the show's hosts and a $5,000 shopping spree in New York City.

"You have to be willing to give yourself -- mind, body and wardrobe," said Brian Eley, the publicity manager of "What Not To Wear," said in an interview.

The U.S. show, a slightly toned-down version of the caustic BBC program of the same name, is in the middle of its second season on TLC. Eley said more than 100,000 people have applied to be on the show.

Tonight's episode is the program's first teenage makeover. Two other students from Blair, Susan Blythe-Goodman and Clarence Turner, will be featured in a promotional edition of the show available only on DVD.

In most episodes, family and friends nominate someone whose fashion sense they feel is about on par with filmmaker Michael Moore's. But in consideration of vulnerable teenage psyches, the show's producers decided to let students at Blair, in Silver Spring, nominate themselves. Producers were familiar with the school because TLC is part of the Silver Spring-based Discovery Networks.

"We didn't want it to be a scene from [the film] 'Mean Girls' where all the popular girls pick on this poor thing," Eley said.

Still, the show can be brutal. Its two hosts ambushed an unsuspecting Johnson-Long during her chemistry class in June as she sat wearing a light blue sweater, black top and short shorts. Their arrival was a mixed blessing.

"You asked for us, so here we are!" London chirped.

"Ouch," Johnson-Long said.

Before show participants get their makeovers, they are subjected to scathing critiques. In Johnson-Long's case, there were the mismatched socks, of course, which she proudly displayed in her nomination video.

In addition, hidden cameras capture candid footage of the fashion victims. One taped scene shows Johnson-Long, who stays fit through cheerleading, wearing a pair of extra-extra-large pants that Kelly tactfully called "billowy." But London was more blunt: "Ugly pants," she said.

Another scene shows Johnson-Long getting ready for school in flowered shorts and a clashing top.

"She's not going to school dressed like that, is she?" Kelly asked.

"I hope not," London said.

A few days after Johnson-Long was selected for the show, she flew to New York with four suitcases filled with her old clothes. The show features a ceremonial trashing of some of her favorite items: the denim overalls that earned her the nickname "Farmer Joe," the blue top she wore to homecoming that the style gurus said looked like scuba gear, the striped pants she had had since middle school.

"Some of the stuff they were saying, I was like, 'I know, I know,' " Johnson-Long said last week while sitting in a Starbucks, decked out in her new clothes. "I had gotten so attached."

But then the fun really began. She spent two days shopping at trendy New York stores -- and never once looked at a price tag.

She bought knee-length skirts and fitted blazers, bright colors and pointy high heels. Then the show's hair stylist smoothed out her locks and fixed the highlights that Johnson-Long had tried to do herself. A makeup artist taught her how to pick bolder colors for her makeup -- coral blush, tinted lip gloss and blue eyeliner.

"I just want people to see me more, you know, as a young adult than a kid," she said during the episode.

By the end of the episode, Johnson-Long proved to the style gurus that she had learned her fashion lesson and was ready to fly home in time to take the SAT college-entrance exam.

"What are you going to wear?" London asked her, jokingly, during the program. "Because that's more important than if you studied for them."

With a gleam in her eye, Johnson-Long responded, "Probably my pajamas."

Then she laughed and gave the answer the style gurus were waiting to hear. "No, I'm just kidding. I'll wear my pajamas only inside the house now," she said.

And as for the SAT? Johnson-Long said she scored a strong 1100 out of a possible 1600 points.

"I just want people to see me more . . . as a young adult than a kid," said Erinn Johnson-Long, center, with show hosts Clinton Kelly and Stacy London.Montgomery Blair High School senior Erinn Johnson-Long went from the hot seat on "What Not to Wear" to a $5,000 spending spree in New York for a trendy, brightly colored wardrobe.