Zachary Harris, center, and Chloe Yokitis, right, both 13, collect signatures on a petition backing measures intended to reduce mold in Virginia schools between classes at George Washington Middle School in Alexandria. (Debbie Truong/The Washington Post)

The runny noses, coughing and headaches flared inside the students’ biology classroom at George Washington Middle School in Northern Virginia — subsiding once the children left.

Bridget Baron said she watched splotches of mold colonize a wall to the right of her desk until, one day, “they all shriveled up and died.” It was a clear sign for the 13-year-old and her classmates at the Alexandria school that something was amiss.

They decided to take action, visiting classrooms to collect samples for a do-it-yourself mold-testing kit they ordered from a laboratory in South Carolina, then shipping the samples off to be analyzed. The results, which arrived a week or two later: 15 classrooms tested positive for mold. Spores were found on classroom ceiling tiles, in a main hallway and, eventually, the weight room, according to lab results.

So the group of 12- and 13-year-olds at the school in the Del Ray neighborhood organized into the Standing for Tomorrow team and spent the past school year fighting for healthier classrooms, meeting with top Alexandria City Public Schools leaders, including Superintendent Gregory C. Hutchings Jr.

They contacted state Sen. Adam P. Ebbin (D-Alexandria) and called the lawmaker’s attention to the severity of the problem inside their school. Ebbin said he is working with the students to address the issue, and introducing legislation in the General Assembly is a possibility.

“Students deserve to be learning in a healthy environment, and staff and teachers who are in the same building year after year deserve to be teaching in a safe environment,” Ebbin said. “These kids are making sure that this issue is dealt with adequately.”

Between classes and during community events, the students have circulated a petition proposing a state law and school board policy update they hope will help rid schools of mold. They have distributed papers with a QR code that leads to the Standing for Tomorrow website.

“We’re just middle school students, and we don’t really have that much experience in this, but if we band together and we stick together to advocate for what we believe in, then we can change something,” said Chloe Yokitis, 13, the group’s communications director.

Ben Delnegro, a bespectacled 13-year-old, said school should be a haven. “It seemed weird how a place where we were meant to be safe and we’re able to learn had something that could cause serious ailments.”

Some people with mold sensitivity experience stuffy noses, throat irritation, coughing or wheezing and eye irritation, according to the federal Centers for Disease Control and Prevention. People who are allergic to mold, which grows where there is moisture, may have more serious reactions.

The Alexandria school system said it supports the students’ activism and noted it has “rigorous” processes in place to ensure mold is treated as quickly as possible once it is discovered in schools. The school system alerts employees and students when it learns about the presence of mold.

“We have some aging buildings that are costly to maintain. The excessive rain this year has had a toll on our aging buildings,” Alexandria schools spokeswoman Helen Lloyd said. “School systems with aging buildings are constantly balancing the need for improving the physical and educational environment in the schools.”

The George Washington Middle School students said they were relocated from their science classroom to a multipurpose room in the school library from the end of September to the middle of March so mold could be removed. But the students said mold began to regrow on the classroom walls in early June.

Schools in Virginia and throughout the country are bedeviled by old and deteriorating buildings and a chronic lack of funding to renovate or rebuild. The Alexandria students want to be clear: They do not blame the mold growth on the workers who maintain their schools.

“We strongly believe that this issue of mold in schools isn’t because of the . . . facilities department. It’s because of the lack of funding at a city and a state level and also because of the recent increase in rain,” Chloe said.

Bridget added: “They’re doing everything that they can under the circumstances, but as they’ve been grossly underfunded for the past 20 years or so, there isn’t too much they can do.”

Mary Breslin, the students’ science teacher, said her students made her realize she had abdicated her responsibility as a city resident. Her failure to advocate for enough money to maintain school buildings led to a“toxic learning environment” her young son will inherit.

“The passion these students have in being scientists and using science to improve their school is remarkable,” Breslin said in an email. “This year, I’ve become their student as I’ve watched them navigate a pathway of change.”

The students’ findings earned regional science fair accolades, including a first-place finish in the Northern Virginia Regional Science and Engineering Fair, along with praise from school system officials.

The middle school students said they distilled important lessons about using science to solve problems and learned to use their voices.

“I’m mainly someone who speaks out in front of children. But in front of adults, it’s really nerve-racking. I learned public speaking in front of elders,” Veronica Holguin, 12, said. “It’s opened me up to the possibilities that if I do this, I can do something else and something bigger later in my life.”