Jon Backhouse, a design and technology teacher at the centre, which has 30 children in Years 10 and 11, had previously worked in Romania for eight years, training orphans in woodwork, joinery, electronics and engineering workshops. He realised that his pupils would benefit from meeting people more disadvantaged than themselves, but their behavioural difficulties always made it a risky business.
"All the pupils here have been excluded from mainstream education or have been at risk of exclusion," he says. "If I'd been told beforehand that four of them would be starting work at 5.30am to get the playground finished in time, or that our lads would ask a disabled Romanian girl up to dance so she'd feel part of the last night celebrations, I wouldn't have believed it."
This summer was the third year pupils from the centre had gone to Romania. On the first trip, nine Year 11 pupils were selected to go. Some had never been out of Somerset before. For others, it was their first time on a train, let alone a plane.
Once there, the English pupils learnt survival skills in the forest, swam in the mountain lakes and explored the country. They also joined forces with the young Romanians, aged 14 to 29, from the orphanage where Jon had worked, and got busy refurbishing a poor, rural school's classroom and playground. Some worked 12 to 18-hour days to get the project finished in time. In addition, they taught the kindergarten children nursery rhymes and craft activities.
"Our nine young people, rejected from school and earmarked as trouble, were superb," says Jon. "There were obvious language problems, but with lots of hand signals they worked really well together, especially on the practical activities."
The Romanians' hard-hitting life stories also affected the pupils. During Nicolae Ceausescu's 24-year reign as the country's communist dictator, Romanian women were told to have at least five children, even though they could ill-afford to feed them - not least because food was being exported to help pay off the national debt. The result was 150,000 babies brought up in squalid, overflowing state-run orphanages. Meeting the human face of these statistics was a moving experience. "They were taken aback by what some of the guys had been through," says Jon.
"It was a good opportunity to talk and be reflective of their own lives. A lot who felt pretty hard done by began to realise just how lucky they are. Others recognised similarities, such as how they've all been rejected by society. It fostered a spirit of international understanding."
A second trip followed the next year, but this summer the PRU went one step further: it raised pound;2,000 and bought land in Baia Mare, in the north-west of the country. The site, dubbed Prumania by the centre, is surrounded by woodland and a gentle river, and was devoid of all creature comforts including cooking, washing, toilet and showering facilities.
Such basic camping fostered a real "spirit of invention" among the pupils, who made their own chairs, flip-flops, hammocks and snorkels from wood, spare sleeping mats and plastic bottles, as well as anything else they could find.
"So-called 'difficult' boys were getting up early to light the stove and make fresh bread for the rest of the team," says Jon. By the second day a composting toilet was finished along with a solar powered extractor fan. A giant 10-metre yurt (a circular Mongolian tent) was also erected as the central communal area, with a kitchen, benches and tables also going up quickly.
In addition to the creation of Prumania, which aims to become a permanent international youth centre on the site, the pupils constructed a giant mural for the local school, together with a wooden pirate ship in the playground - all in the mid-30C heat. When the pupils saw the kindergarten children's delight on the last day, there was a tangible sense of achievement among the group, says Jon.
"The biggest thing was that they realised their efforts could improve the lives of others," he adds. "They could make other people happy. It was quite dramatic."
It was not all plain sailing. The pupils were working hard in a different environment; they couldn't speak the language; there was no flushing toilet and they couldn't just go home when the going got tough.
"They worked like Trojans," says Ian Martin, deputy head of The Mendip Centre. "They endured a heat wave, were eaten alive by mosquitoes and were sleeping in tents even though they were afraid of bears and snakes. They came back proud of themselves and the work they'd done. They were thoughtful, humbled and enthused."
Simply through having fun without the help of drugs or alcohol was an achievement for some habitual users. "Managing the whole week without a drink was a surprise, because it was still a really good laugh," says one participant. Another adds: "It has made me appreciate another country's way of life and I'm seriously considering going back to do voluntary work when I'm a bit older."
Jack Trussell, 19, used to go to The Mendip Centre, and was recruited as a group leader on the most recent trip. Having been excluded from two mainstream schools and one PRU, he is described by Ian as one of the centre's "more troubled" pupils who came as close to exclusion from the centre as it was possible to get.
But Jack loved the welcoming atmosphere of the centre and soon excelled. He has now just finished a national certificate in outdoor education at a college in North Wales and was described as an "absolute star" in Romania.
"It really tested my capabilities," he says. "I had to be responsible and not muck about with the other kids because I was there to help the teachers. That was a new experience for me, but I really enjoyed it."
He is particularly pleased with the bond between the English and the Romanians and the way they worked as a team. "It made me appreciate how easy we have got it," he says. "Others have so much less, but whinge less as well."
The rest of the group shares Jack's sentiments. There has been a subtle shift in attitude towards Eastern European workers in Britain following the trip, according to Jon. From being quite negative about Poles "stealing our jobs", there is now a new appreciation about why they may need to leave their home country.
But the most pleasing outcome in his eyes has been the way the pupils' self-esteem has grown. "It's quite dramatic seeing the incredible amount we achieved in one week. When the kids surveyed their work, they were rightly proud. They know now that they can face pretty hard and uncomfortable challenges and they can cope. In the long-term, that's going to have a significant impact on their self-confidence."