Dressed in a cap-sleeve blouse and black knee-skimming skirt, she is talking about the new student dress code at her high school. The policy, drafted by faculty over the summer, expressly prohibits sleeveless shirts.

Bare shoulders, the administrators posit, are a distraction at the 1,413-student Timberlane Regional High School in Plaistow, N.H. 

“I don’t see how shoulders are a distraction,” said Skerry, who was branded a scofflaw by high school principal Donald H. Woodworth for wearing her cap-sleeve blouse to class the first day of school. “But that’s what the administrators keep saying, ‘Bare arms are a distraction in class.’”

Upset and embarrassed, Skerry, a straight-A student who speaks with a maturity that belies her 17 years, took her case to the School Board on Sept. 20 and has launched an online campaign to amend the dress code. Her Facebook page, wittily dubbed “The Right to BARE Arms,” promotes a petition that asks school officials to allow students to don sensible sleeveless dresses and tops. Nearly 300 students have signed it.

“In a school with limited air conditioning, for optimum learning to take place, the students need to be comfortable,” the petition states. It urges the administration to “take all necessary action to reinstate sleeveless tops and dresses” into the dress code, including “all sleeveless shirts and dresses that cover the bra strap and Timberlane sports jerseys.”

Superintendent Earl F. Metzler 2d, who took over leadership of the Timberlane and Hampstead school systems Aug. 28, said the dress code was drafted by the high school’s climate committee, a body that was formed over the summer to improve the learning environment in the building.

In addition to updating the school’s dress code, the committee also adopted a new attendance policy, School Board members said.

The high school, which serves the communities of Atkinson, Danville, Plaistow, and Sandown, has been identified as a “school in need of improvement” for failing to meet federal benchmarks for student performance on the New England Common Assessment Program exam, the equivalent of the Massachusetts Comprehensive Assessment System test.

The goal of the new policies was to make the school’s expectations clear, Metzler said. According to Timberlane Regional School Board chairman Robert Collins, a Danville resident who has been on the board since 2008, the previous dress code included vague language that made enforcement difficult.

Under the new policy on proper attire, all students are “required to wear tops . . . that have sleeves, a modest neckline . . . and that are long enough to cover beyond their waist. The length of shorts, skirts, or dresses may be no shorter than mid-thigh.”

Students who violate the dress code are asked to change their clothing and may face disciplinary action, including detention and administrative probation, according to Timberlane’s student handbook. Skerry and her supporters like to point out that many female role models — including Michelle Obama, British actress and humanitarian Audrey Hepburn, and singer-songwriter Taylor Swift — often favor sleeveless fashions.

“If the first lady can show her shoulders, my daughters can too,” wrote Sandy Desmond, a follower of the Facebook page. “This is not acceptable! The school should focus more on empowering our daughters to be strong, intelligent, and independant [sic],” she wrote.

Skerry, a junior nicknamed Bitsy who is serving her third year as secretary for the class of 2014, has attracted national attention as news outlets as far away as California report on her campaign. One woman from nearby Kingston, N.H., said she was so impressed by Skerry that she named her pet chicken Bitsy, after the English honor society student.

But at Timberlane, Metzler said there has been an outpouring of support for a dress code.

“Many students and parents appreciate that we’re making it clear that we have high expectations,” he said.

There have been few violations of the dress code and no harsh disciplinary actions have been necessary, he said.

After Skerry addressed the School Board, Metzler asked Woodworth to reconvene the climate committee to review the new dress code — this time, with student input.