The flag over Ballikinrain Castle is one of many patches of green in the wooded grounds of the Stirling school, run by the Church of Scotland. But right now it's the one that pupils and staff are most proud of.
Awarded by Eco-Schools Scotland, the flag shows that a school is "committed to the highest standards in environmental education and management". It is the first award of its kind for Ballikinrain School, and the first for any residential school in Scotland for youngsters with emotional and behavioural difficulties.
"The pupils are clearly central to the environmental work here," says Eco-Schools assessment officer Anne Black. "That's what we're looking for. We want to see that pupils are engaged, that they have a voice, that they are driving things forward. I particularly liked how they let us sit in on the committee meeting at the start of the day."
Chaired by Declan Laird, 13, that meeting covered various topics, from risk assessment of activities and whether dogs are allowed in school ("Yes, if we can keep them out of the kitchen," says Declan - "which is hard."), to a review of the past year's environmental work.
"Where have we seen the biggest improvement?" Eco-Schools co- ordinator Lisa Steven asks the committee. "The courtyard," say the lads, referring visitors to before-and-after photographs of pockmarked tarmac at the rear of the old building, now dark and smooth.
"We used a power-washer and scrapers," says Declan. "It would have cost a bit of money to get it done, so we did it ourselves. We've also been making sure people wrap their chewing gum in paper now and throw it in the bin."
Ballikinrain pupils can be unpredictable, says head of education Kyle Fleming. Illness, bereavement and inadequate parenting can take their toll on pupils with whom mainstream school has failed to cope.
"They've not had the chance to enjoy being children," says Mr Fleming. "They have had to grow up too soon. Getting them outdoors in these wonderful grounds often helps to calm them down."
But inside the school, emotions can run high. So giving youngsters all this responsibility was a risk, says Lisa Steven. "I was a wee bit nervous," she adds. "Last night, in fact, one of the boys was refusing to take part at all. But he did and he's done fantastically well."
"Would you like to tell them about energy saving?" Declan asks fellow pupil Johnnie Munro, 13, who draws attention to a chart in the handout. "We were set a challenge and we succeeded by monitoring electricity using the meters in the basement," Johnnie explains.
"Last year, we saved nearly Pounds 700 by putting posters up and reminding people to switch lights and things off - and by using games machines that switch themselves off. They use a lot of electricity."
Ms Steven responds: "If the electricity companies didn't keep putting their prices up, we'd have saved even more."
In its first year at Ballikinrain, the environmental work consisted of one-week projects, says science teacher Derek England, but it now "pervades the whole ethos".
"We have had longer blocks of study this year and bigger projects. We've been looking at sustainable energy sources and we're building a solar water heater out of parts we have ordered and will put together ourselves," he says.
Jordan Cattrell, 15, has been especially enthusiastic about this, says Mr England, and recently accompanied him to one of the most spectacular sustainable energy schemes in Scotland - the hydro-electric power station at Ben Cruachan. "It was very big," says Jordan. "I wrote a thank-you letter when we got back, because everyone was so kind.
"I'm not on the committee because I wasn't interested at first. But when I saw what they were doing, I thought I'd give it try. I'm glad I did. It's fun. It gives a good impression of the school - makes it look better. That's important, I think."
Such is the interest around Scotland in Eco-Schools that former chemistry teacher Anne Black, one of two full-time assessors, now carries out three to four assessments a week. "I could be doing it every day, because we are getting busier all the time," she says.
"Over 750 schools already have a green flag, which comes up for renewal every two years, and new schools are coming on board all the time. I love seeing all the work they do in the schools. And days like today are about more than just assessment. They are a celebration, for pupils and staff, of all the work they have done towards getting their own green flag."
Ballikinrain School is run by Crossreach, the Church of Scotland's social care agency.