The girls wear them under their uniforms in lieu of the lace-trimmed slips their mothers wore when they were in school.
And if they show just a bit, well . . .
"It wouldn't be fun if they didn't show just a little bit," was the anonymous, tongue-in-cheek comment by a school administrator.
Boxer shorts are certainly not part of the official school dress code, but the girls insist they are an essential part of their wardrobe.
"They are made of light material, and they are comfortable in any season," said Karyn Bongard, 16, a junior at St. Hubert Catholic High School for Girls in Northeast Philadelphia, explaining the practicality of the fad.
But, of course, there are fashion reasons as well.
Ann Marie Kuvik, 16, a junior at St. Hubert, said she wore boxer shorts simply because they were in style. Wearing them peeking below her hemline, ''shows you know fashion," she said.
To be up with this hot look, girls go all out to find a variety of shorts. They scour flea markets, check out the men's department of every department store around and, when visiting area universities, stop at the book and
college-paraphernalia shops to snap up boxers covered with the school's logo.
It's not unusual for girls to own as many as 30 pairs of trendy undershorts. Some girls wear them to fit their mood or to show their support for their favorite athletic team.
Local Catholic school administrators are amused by this fad, but keep it in check by politely chiding the girls to "pull up their slips."
"Teenagers do unexpected things and crazy things for fun," said Sister Joan Rychalsky, director of guidance at Little Flower in Northeast Philadelphia. "When you see them (boxers), it's just part of the unexpected in dealing with adolescents."
Recently, Dorothy Freeman, 16, a junior at Little Flower, was sporting yellow flannel boxers under her maroon uniform. "They are comfortable, and I just don't like wearing a slip," said Freeman, whose mother is not thrilled by her daughter's donning masculine underthings.
"My mom does tell me to pull them up, but that doesn't stop me from wearing them," she said.
Freeman's lingerie drawer is packed with a different pair of boxers for each day of the month. Her mother reluctantly pays the price.
Prices for boxers can range as high as $35 for novelty silks, but on a more pragmatic level, they can be picked up for as little as $4 for plain cotton. Maureen Connolly, 16, a Little Flower senior, is a collector. She covets undershorts that are covered with logos of Philadelphia sports teams as well as the logos of local universities such as Temple, St. Joseph's and La Salle. She said the boxers are "warm and comfortable" and they allow her the freedom to sit anyway - without worrying about being immodest.
Connolly has managed to add to her collection, picking up shorts in the course of searching for a university to attend after graduation.
But she's not the only one in her Northeast Philadelphia household who wears boxers. Her dad, Edward Connolly, is a boxer man - though he prefers the plain cotton style.
He has no problems with his daughter's wearing the same kind of underwear as he does: "I think her wearing boxers is very good because it is a sign of a young lady who has a sense of modesty. After all, it is a trend and it's not like she is the only person who is wearing them," said Edward Connolly.
Connolly and the girls at Little Flower know that they'd better beware of the uniform fashion patrol - school officials who insist that the shorts not be visible beneath the hemline of their skirts.
School principal Marie Gallagher, like other Catholic school officials, sees the fad as harmless, but says the shorts are not part of the dress code and should, like most underclothes, be kept out of sight.
"It's one of the fads you have to get used to when you are a principal," she said. "Teenagers are going to find someway to be unique. This is my 20th year of teaching and I have seen lots of fads including feather earrings, long earrings. . . . In 1987 they were wearing jams; now it's boxer shorts with flannel."
At St. Hubert, Sister Marita Carmel has developed several lines to remind her students to hike their shorts.
"I think they look awful and they drive me crazy, but I keep it low-key and just remind them to pull them up out of sight," said Sister Carmel. She might ask: "Where's the tennis match? or "Could you lower your skirts, ladies?"
She said the fad spread quickly. "I see them on the El on girls from Hallahan (J.W. Hallahan Catholic High School for Girls) and I see them everywhere."
So where did this fashion trend come from?
"I started wearing them because my friends wear them and we all buy them in the men's department. It's just the thing to do," said Dawn Carroll, 14, an O'Hara freshman, who said the correct way to wear them is with half an inch showing below the skirt. Carroll has paid from $12 for a three-pack of plain at Sears to $12 for a flannel pair from Strawbridge's, and $14 for Swarthmore logo shorts.
A few years ago, teenage girls in some public schools began sporting boxers as shorts during warm weather. Catholic school girls took up the trend about three years ago, but recently it has flourished.
Nobody seems to know exactly where the trend began, though some speculate that it came from professional dancers who wore boxers in videos. Others say it may have trickled down from college-age women who were wearing them in the late 1980s.
Companies that produce men's underwear say they became aware a few years ago that females were a big part of the market for men's boxers.
"Women liked the colors and the comfort and they started buying and wearing men's boxers over their bathing suits and as leisure clothing," said Art DeCesaro, senior vice president for sales at Jockey International, one of the largest U.S. men's underwear manufacturers.
"I've never heard of them being worn under uniforms before, but women and girls' wearing boxer shorts is a trend across America," he said.
Just as the local Catholic students say they wear boxers for comfort, DeCesaro said the company's line of women's underwear "Jockey for Her" was born in response to women who requested more comfortable clothing.
"We had women writing letters saying they were buying our men's Elance line so frequently that we decided to make a line for women," said DeCesaro.
In recent years, novelty boxers have become more and more prevalent in the stores. Jockey has its own novelties, flannels and silks. But Jockey is also competing against such companies as Joe Boxer and Charles Goodnight, which sell the novelty variety.
Liz Brown, a secretary at Notre Dame, said she hit the men's departments when searching for her daughters' boxers and was surprised to see so many styles.
"Originally they were made for fathers and you could tell," said Brown.
"Now there are silk ones and flannel ones for the cold weather. Underneath the uniform they are a real hot commodity," she said.