On Friday afternoons, a low rumble fills the halls of Parr's Ridge Elementary.
The source: large gray trash bins, rolled by a squad of second-graders and parents at the Mount Airy school.
The green letters and circle of arrows on their white aprons state their purpose. They are the Green Team, the school's recycling crew, which collects scores of pounds of paper - construction, copy, notebook - each week.
Launched last fall, the team has mushroomed from an effort to ensure "we recycle" became a schoolwide practice to one that aims to spread such thinking throughout the district.
"It's been a great start," said Erin Tunkel, the Parr's Ridge mother who, with second-grade son Ryan, 7, developed the concept. "We need to stop being such heavy consumers. We need to just be aware of what we're buying ... and what we're throwing away."
Children can help make those small changes, Tunkel said, by talking to their parents and encouraging them to modify habits, once they learn the realities of "the dump" - where trash goes, but doesn't necessarily go away.
Such thinking echoes that of county officials, who have spent recent months talking trash, and the best way to dispose of it. Many have emphasized the need to ramp up the recycling rate of about 30 percent - something a recently approved recycling manager position is meant to help jump-start.
But throughout the debate, there has been an emphasis on the importance of education - and targeting the young.
"Recycling is something that needs to be repeated," said J. Michael Evans, Carroll's public works director. Schoolchildren are "the best repeaters," he added, "because they come home enthusiastic about something, and they show Mom and Dad how to do it, and they sort of police it."
The school system has been recycling paper and cardboard for a while, said Raymond Prokop, director of facilities. More recently, with the county's introduction of single-stream recycling, that has expanded to other items, he said.
"There seems to be quite a bit of interest out in the schools," Prokop said, adding that kids, in particular, appear to be driving the enthusiasm. "We encourage it."
The Green Team is about "moving out of the conversation into action," said Teresa Shattuck, a parent at Mount Airy Elementary, who helped start that school's effort in March. At that school, fifth-graders troop through the halls each week, collecting paper and bottles.
"It doesn't take that much effort," Shattuck said. "It's really just a matter of finding folks who have the will, the time, the energy to take this on."
Tunkel and Shattuck said they also teach students more about recycling, discussing where the items go, and how long things take to break down.
"Hopefully that hits home with them," Tunkel said.
One thing that has caught on, she said, is the kids' enthusiasm for the teams.
On a recent afternoon at Parr's Ridge, Kyle Strong, 8, quietly slipped into a classroom where students were watching a video.
"He's coming for our recycling," a teacher in the room said, responding to the inquisitive eyes turned to Kyle.
The second-grader hefted a box painted blue and sporting a white recycling logo and dumped its multicolored paper contents into a bin. He tiptoed back to return the box, before heading to the next room.
Later, he and Ryan joined their peers at a large scale in a health room, where Tunkel and two other mothers helped them weigh the full large black trash bags to determine how much they collected.
"Wow - 38, you guys," said parent Jennifer McAninley, of one bag. Niya Pattasseril, 8, jotted down the figure, tallying their total with the help of Nico Lindsay, 8.
The day's intake: 171 pounds. And, gathering around the chart mounted on a wall to track the recycling they had amassed each week, they soon discovered they had surpassed 5,000 pounds.
Elements like the chart, which ties back to math lessons, make the exercise meaningful to the students, said Ann Marie Blonkowski, the school's principal.
"We all need to be recycling," Blonkowski said. "It only makes sense that we model it here at our school."
The school plans to expand the program next year, she said, with a recycling bin for community use.
Ryan, for one, said he wasn't surprised at the 5,000-plus pounds the team has picked up this year. He and his peers said they have become more conscientious about their own trash-disposal habits.
Niya tells her 2-year-old sister to "go to the garage and put it in the blue bin" when paper and plastic bottles are involved, she said.
Kiera McAninley, 8, said she uses scrap paper before she pulls out a new piece.
Nico's mother, LeeAnn Leshko-Lindsay, said her son is at times even more diligent than she already is about recycling, even noting that they could do so with their toothpaste tubes.
"If the schools do it, and the kids become so conditioned, then it becomes natural," she said.
"You see all the difference one school can make in the community," Jennifer McAninley said.
Next year, Tunkel said, the team is looking into a program that pays the school based on the amount of recycling collected.
Beyond that, she would like to see the Green Team model - which has received a certificate of recognition from the U.S. Environmental Protection Agency's regional office - adopted at other schools, she said.
"We need to be aware of how much [kids] can really do and how much change they're capable of," Tunkel said. "Maybe there'll be a ripple effect."