What began with a few yards of tartan has sparked an international debate about freedom, symbols and cultural dress. More than 1,600 people have signed an Internet petition seeking an apology for the high school senior.
Scots in the United States are assembling a traditional ensemble they hope the student will wear to the prom, and his family is trying to change the school's dress code policy.
"It's a kilt. It's going to turn heads, but I never believed it would have become what it is," Warmack said.
Other schools around the country also have wrestled with the issue. A principal in Victoria, Texas, ordered two boys into "more appropriate" attire when they wore kilts to school in 1992, saying: "I know kilts. Those weren't kilts and the boys aren't Scots."
In 1993, a student in Fayette County, Ga., was not allowed to enter his prom at McIntosh High School because he showed up in a kilt and refused to change clothes.
And while they weren't trying to dress in kilts, a few boys were allowed to wear skirts to class at Franklin Community High School in Indiana in 1997, when a superintendent said different people express themselves in different ways.
Warmack, a defensive lineman on the football team, lives in Jackson, a growing, largely middle-class city of about 14,000 people about 110 miles from St. Louis.
He got interested in his family's Scottish ties after seeing Mel Gibson's 1995 movie "Braveheart," about William Wallace's battle to overthrow English rule in 13th century Scotland. Warmack reads books about Scotland and visits Web sites to learn more about his family's genealogy.
He bought a kilt off the Internet to wear to his school's formal "Silver Arrow" dance in November. Warmack said he showed it to a vice principal before the dance, who joked he'd better wear something underneath it, and Warmack assured him he would.
Warmack's parents, Terry and Paula, helped him piece together the rest of his outfit, a white shirt and black tie with white socks and black boots.
"We knew it wasn't the formal regalia," his father said. "We wanted it to be acceptable for the occasion."
After Nathan Warmack and his date posed for pictures, principal Rick McClard, who had not previously seen the kilt, told the student he had to go change. Warmack refused a few times and said the outfit was recognizing his heritage.
Warmack alleges McClard told him: "Well, this is my dance, and I'm not going to have students coming into it looking like clowns." McClard later said he had no recollection of saying that, Warmack's dad said. The principal did not return phone calls seeking comment.
The school district's superintendent, Ron Anderson, said McClard has the authority under the district's dress code policy to judge appropriate dress for extracurricular activities, including dances.
"It's mainly to protect from the possibility of a disruption or something that could be viewed as a disruption," Anderson said.
Several Scottish heritage organizations are angry, saying the kilt is a symbol of Scottish pride and considered formal dress.
"To say the traditional Scottish dress makes you look like a clown is a direct insult to people of Scottish heritage and those who live in Scotland," said Tom Wilson, a Texas commissioner for the Clan Gunn Society of North American, a Scottish heritage organization.
Another Clan Gunn member, Beth Gardner, started an online petition seeking an apology for Warmack. It questions in part the notion that the kilt was a distraction.
"From what? From the intense concentration it takes to dance?"
Scottish groups are hoping they can help him to establish a formal Scottish ensemble that more fully reflects his heritage, including pieces that are being handmade for Warmack in Oklahoma, Georgia and Florida.
Warmack said he's concerned that school officials are just waiting for the situation to blow over, and that the policy won't be changed.
"This has picked up a lot of steam," he said, "but it hasn't really gotten anywhere."