Imagine there’s a dream youth programme that could spirit away your 16-year old, just spat out of the GCSE factory, for three glorious weeks this summer before heading off to college, with brief family reunions each weekend. What would it entail? Days of Tom Sawyer-style raft-building with a bunch of like-minded kids? Canoeing on a lake? Abseiling? Wouldn’t that be perfect after months of their being hunched indoors over work?

What else do our teens often lack? Self-sufficiency? Fine. Stick them in student halls and get them to budget and cook for themselves. Expect crisp-encrusted poultry. And finally, isn’t it time sir and madam did something for someone else? Organise a sponsored three-legged night walk for Stonewall, perhaps, or put on a fun day in a vacant shop in aid of Cash for Kids and the Dogs Trust?

Enough teasing. This programme exists. It’s nationwide, across England and Northern Ireland. Your son or daughter will love it. And it costs a million pounds. That’s a joke — it costs fifty quid. However, it goes by the unglamorous name of National Citizen Service. It’s a Big Society initiative, subsidised by the government, launched in 2011. Since then, 130,000 teens have taken part.

Not quite your sort of thing? Not giving off the whiff of ponies or cricket? Dulwich College, an independent school in London, puts forward 50 boys for it each year. Dr Joseph Spence, the headmaster, moved by its transformative effect on pupils — “every year, different kids come back and talk about where they felt valued’’ — is a passionate advocate.

“What I love about NCS,’’ he says, “is that it’s equally valuable to the rogues and to the virtuous. There are so few opportunities for 16-year-olds in this world of health, safety and risk-assessment.” (Not to mention that four nights at Camp Beaumont can cost over £300.)

“Sixteen is such a great age to get out there: live with people from all different backgrounds, do a project together, do something adventurous together, learn some skills together. It’s so winning and such a wonderful counter to the exam-factory culture they’ve been forced through.”

NCS, run locally in hundreds of locations by a range of programme providers, adheres to a reasonably exact format. In the first week, teens — normally about 60 but divided into groups of 12-15 — stay at an outdoor activity centre, taking part in pursuits such as rock climbing, hiking and archery.

In week two, after returning home for the weekend, they spend four days in university accommodation, living and cooking independently overseen by youth workers and older teens who have done the NCS “leaders course’’ before acting as mentors.

They meet local businesses, might learn first aid courtesy of St John Ambulance, take a course on money management with Barclays or produce a TV report with Sky Skills Academy. In week three, they design a social action project to make a difference in their community and devote at least 30 hours to putting it into practice.

Lydia Cooke, 17, from Staffordshire is a boarder at Rye St Antony, an all-girls school in Oxford. She was expecting to spend her post-GCSE months last year watching TV and lounging about with friends. But then two NCS representatives spoke in her general studies lesson. She gave them her details and soon after, “My mum called: ‘NCS has been on the phone. I’ve just signed you up.’ Oh my goodness,’’ she exclaims, “I am so glad she signed me up. I’ve just made so many incredible friends.”

Turning up at NCS in Rugeley, Staffordshire, she didn’t expect to. “The first day was really daunting. Speaking to all these people, you’d notice they have a different accent and the first thing you talk about is where do you go to school. If someone said a certain school you’d think in the back of your mind, ‘Hmm’, and people were thinking that about me. But even on the first day we realised: hang on, we’re not different. We all had the same values. We all believed in the same things.”

While thousands of 16-year-olds realise they are “all for one and one for all” within hours, the uptake from independent schools despite NCS addressing the Headmasters’ and Headmistresses’ Conference has been disappointing. It indicates, says Spence, a slowness to grasp “what a great boon this can be for everyone. We live in a stratified society still, and there are those barriers, and it’s as much as anything, where you live, what sort of school you go to, what your family tradition is.I think if you catch them at that age they realise that they share more than divides them.’’

He suspects that some heads of independent schools like him assume “it must be to do with getting to people who need that’’. He says this complacency is occasionally echoed by parents: “Some of the more difficult conversations I have involve [the assumption], yes, ‘But surely a lot of your boys have these chances anyway.’ ” For the record, a Duke of Edinburgh Award, brilliant though it is, requires a far longer commitment, is often undertaken with friends and can be costly.

“NCS is unique,” Spence says. “So many of the things we do these days lead to inevitable success. If you embark on Duke of Edinburgh, as long as you go through the form, you will get there. You join a scout group, they will help you there. NCS is giving kids a chance to project themselves and sometimes fail. Everything else feels relatively safe.

“It’s this sense of finding what is your skill, what can you contribute? It’s learning something of mutuality, how important it is to play to your strengths. And at the end of the summer, it’s not all a story of ‘oh look, there’s another 24 gold medals won’.”

Speaking to teens who have taken part convinces me that my own son must attend in three summers’ time. Jay Daniells, 18, from Workington, Cumbria, who attended NCS in Ullswater (for activities), and Whitehaven (for independent living) in the Lake District, gives an exhilaratingaccount. “Prior to NCS, I was very comfortable in my own friend group: people who went to the same school or lived round the corner. I never really put myself out there to talk to new people. It was a sudden surge of all these people. Quite scary, but it was surprising to me how naturally I made friends. By the end of it we were like one big family.”

Daniells enjoyed every minute. The budgeting: “I found out I was really bad with money.’’ The acquiring of life-skills: “We went to our local magistrate court and took part in a mock trial. A person called Barry had attacked someone in the park. We had witness statements. Everybody had to act — it was brilliant.’’

And of course, the cooking: “Everyone’s favourite crisps were Doritos. We decided to make Doritos-breaded chicken, but we couldn’t get them to stick on.’’ Fortunately, they had the good sense to consult a cookery student in another group. Daniells says: “It really was as simple as mayonnaise mixed with milk.”

Louise Harris, 16, who has got into Dungeons & Dragons since bonding with Daniells at NCS, says: “He brought me out of my shell.’’ She in turn introduced him to 1980s rock. At first, she recalls, he and his friends “didn’t look like the kind of people I’d usually hang out with, but he’s one of the nicest guys I’ve ever met”.

Some experiences are priceless and Spence is amazed that many of his colleagues in other independent schools haven’t grasped this. It teaches children that life isn’t just about exams, revision and going from A to Z, he says, and it offers a far deeper life experience than a work placement set up by some family contact.

Cooke, believes that many independent pupils are held back by their shyness at meeting other types of teenagers. “It’s not popular at my school. The concept of meeting people from different backgrounds is too much out of some peoples’ comfort zones. I think they’re completely wrong. I would just encourage it so much. It’s so great.’’

Cooke’s mother, Paula, a teacher, agrees: “NCS has opened up this massive world of different people that maybe Lydia would not have met at this age, maybe because of the limitations of being at a boarding school. And I think that is really, really important.’’

Sarish Saghir, 17, who is a Muslim and attends a comprehensive in Bradford attended her local NCS last year. She feared “that people would judge me. People from different cultures, backgrounds, ethnic minorities, posh people, normal people, estate people, a whole mixture of people. Initially I thought I’d keep out of their way, but you open up and you realise: don’t judge a book by its cover.’’

Saghir’s favourite activity was rafting. “We had to build our own raft from four planks of wood and some barrels. It was a total failure, but we were all working together. It was such a happy atmosphere. It’s not always about winning.’

Like all her peers, Saghir becomes most animated when describing her team’s community project. “We have a lot of homeless people in Bradford,’’ she says and this was their focus, which her team continued work on after the summer. They secured £2,000 funding, then met each Saturday in the library to plan a strategy.

We bought, recalls Saghir, “250 pairs of socks, 60 fleeces, 100 long johns, 100 hats, 100 gloves, scarves, countless food items, 100 bars of soap, 100 toothbrushes. We went to a homeless shelter, we gave 120 presents. Then we did a raffle. We picked two winners; one man, one woman, bought them brand new clothes, shoes, coat.

“We arranged for the lady to get her hair done at a top salon, and we took them out for a meal at a restaurant. And in return we asked to hear about their stories. They told us about living in poverty and not being able to feed their children. It opened our eyes,’’ Saghir adds.

Spence is so keen for more independent school pupils to benefit from NCS that he’ll even overlook any comments such as “that’ll look good on your CV’’. “Of course that’s the wrong motivation but if it comes from that let that be the motivation, and when those children find something that really ignites them they’ll forget that they only did it to put it on the Ucas form.’’

However, parents who believe the two weeks at Kings organised by a family connection is a safer career path, be warned. Spence says: “I think we’re maybe over the period in which people fell for the long CV and we’re at a time now where people look at the rounded person. When I look at the way [many universities are] interviewing now, it’s evident they’ve had 20 years of CVs that say, ‘By the time I was 18, I’d climbed the Himalayas, cured cancer, and all the rest in between.’ ’’ It’s not, adds Spence, a matter of “what did you do?” but “what has it done to change you?”

Ashish Ramuni, 18, a thoughtful young man, attending a fee-paying grammar school in Bury, Manchester, says: “NCS has actually changed my life.’’ Keen that this isn’t swallowed whole as a cliché, he adds: “A statement which can rarely be said with genuine gravity. I do mean it.’’

He was studying biology, chemistry, further maths and French, intending to follow his parents into medicine. But NCS fuelled a passion for public speaking, and a meeting with Nick Boles MP on the NCS Leaders Programme (in which graduates develop leadership skills and become ambassadors for the scheme) “made me feel like I could effect social change. So I changed from biology and chemistry to politics and economics. And now I hope to do a degree in PPE at university.”

It’s clear that these teens even now can’t believe their good fortune. Ramuni describes the end-of-the-day “reflection period with our group leader’’, involving the True awards. “True stood for teamwork, respect, understanding and empathy. Patronising as it might sound,’’ he says, “it really wasn’t. It was mentioned to us and we had to reflect on whether we’d displayed those skills. In a subconscious way it helped us develop them.”

Surely such opportunities arise naturally at school? Ramuni says: “I’ve always felt what you are in your fifth year at school, your GCSE year, is the sum of all you’ve been for the past five years. And at any given point, we are not the sum of what we’ve been for the last five years. With NCS, it was a fresh new start. You were able to be just you, as you are, in that moment.”

And given that rare freedom, these children connected. Recently, Ramuni met up with his group to discuss their social action project. He says: “It served to remind us of how much we absolutely loved each other.’’