Principal Deb Black said she didn’t think it would be a big deal.

After she and fellow administrators at Skyview High School noticed that girls were shedding jeans for form-fitting leggings, they decided to clear up some things.

They wrote this into the handbook over the summer: “Leggings, jeggings, and tights ARE NOT pants and must be worn with dress code appropriate shorts, skirts, dresses, or pants.”

But the policy change has roused some students, including junior Dayah Dover, who went to the school board Monday to say the code unfairly targets and shames young women.

“I’m planning on raising some hell,” Dover said Thursday.

While not technically a ban, the dress code requires that a girl who wears spandex or nylon pants also put on a top that covers her bottom.

“So that every line and curve isn’t showing,” Black said. “It’s not appropriate attire for school. I can’t imagine myself coming to school wearing yoga pants and a T-shirt.”

Yet that same attire has quickly become a mainstay in young women’s wardrobes, marketed as a versatile, comfortable and sexy alternative to jeans. Sales of jeans dropped last year for the first time in over a decade, driven primarily by women opting for yoga pants, leggings and similar “active wear,” the Associated Press reported last week. Headlines like “Jean Sales Fade thanks to Yoga Pants” and “Yoga Pants are the New Jeans” have graced newspapers across the country.

Just as quickly, the tight, stretchy material has emerged as the latest fault line in the war over school dress codes. Schools that have moved to curb the practice are inspiring student activists from California to Massachusetts. Last spring, teens in Illinois decried a ban on the pants at their middle school by wearing them en mass and carrying signs like, “Are my pants lowering your test scores?”

Billings School District 2 disallows articles of clothing that “materially or substantially disrupt the educational process” or cause a health or safety concern. Each school determines exactly what to prohibit.

Spaghetti straps, bare midriffs, short shorts, exposed boxers, bandannas (except on school spirit days), shirts displaying weapons or alcohol, trench coats, slippers and muscle shirts are among the casualties within Billings high schools. Each code is slightly different, and Skyview is the first to place restrictions on leggings and yoga pants.

Dover doesn’t mince words in describing what she thinks about the latest addition.

“It’s completely sexist and misogynistic,” she said. “This tells women that our bodies are something that needs to be hidden.”

Dover is referring to the justification given by school administrators, including Skyview’s Black, that thin, tight pants can be a distraction to other students — namely, boys.

“News flash: Everybody has a butt. Just being a female is distracting, apparently,” Dover said. “If any part of your figure is emphasized ... that is not allowed.”

To that criticism she adds the preception that guys seem to be held to less imposing standards — sleeveless T-shirts for boys are allowed at Skyview — as are athletes wearing their uniforms. Dover notes that college students often wear casual clothes to class, including yoga pants, because “school is where we come to learn,” and girls should be able to feel comfortable while doing so.

Dover doesn’t think any clothing should be banned, so long as it doesn’t show underwear. “All it does is express our personality,” she said.

Black said she doesn’t seek to be a vigilant dress-code enforcer, but argues that making sure students are dressed “appropriately” is also a part of the education the school provides.

“It always comes back to us, ‘well, this isn’t a workplace.’ Well, for right now it is, and we still need to teach those workplace skills,” Black said. “We have to be able to have some direction for our kids, because they are kids.”

Administrators announced the policy change during class meetings by assistant principals to discuss rules and expectations for the year.

No one has been sent home for violating the new code, but Black said she has asked several students to put on a longer top. If the student doesn’t have one, she can wear one of the shirts Black stores in the main office.

“We keep a supply,” she said.

She did the same thing when sagging pants were popular with boys, stashing zip ties in her desk drawer.

The replacement clothes, and the whole process of being “dress-coded,” isn’t intended to embarrass the offending student, Black said. Students are asked to come to the office or sent there by a teacher, where an administrator talks things over.

Dover said the method of enforcement doesn’t matter, because the policies themselves “tell us that we shouldn’t be proud to be ourselves.”

A varsity debater and a self-described activist, Dover said she took her concerns straight to the SD2 board, hoping its members could prompt a change. A petition she started on change.org had around 200 signatures Thursday.

She also went shopping this week to buy her first pair of yoga pants, which she has worn to class for the past couple of days.

And Friday, she said, a group of Skyview students — girls and guys — planned to join her.