We had barely begun a long truck journey across the dirt roads of Paraguay’s vast Chaco wilderness when a tyre sprang a leak. After lurching along “like an armadillo on speed”, jostled together “like pitbulls fighting in a pair of tights” (to quote team member Andy), we admitted defeat. It now turned out that all the tyres were worn and the only spare had already been used following an encounter with a spike.

Driver Orlando’s pump “let out less air than Roddy’s rear” (Andy again) so two hours and no traffic later, hot, and with diminishing supplies of water, we started hallucinating about organising an air lift out with our BT satellite phone. Luckily, a distant truck proved not to be a mirage and its compressor soon put our tyre to rights.

The ability to rise above unexpected mishaps is intrinsic to “overseas phases” (or expeditions). This one is part of the Fulcrum Challenge, founded by the Scientific Exploration Society and sponsored by British Airways and the Institute of Directors among others as a means of “investing in the leaders of the future”. In the team are 12 girls and six boys aged 17 to 18 drawn from Scottish schools, director John Hunt and six leaders including headteacher John Lowe, business entrepreneur Gary McEwan and Roddy Dyce of Young Enterprise Scotland (see box). During the two-week venture, each student will research a project to be written up for presentation to BA. Our guide, James Wright, tells them all they need to know about Paraguay’s wildlife, people, history and political background.

James was 14 the first time he went walkabout across the Chaco’s palm savannah wetlands and dense, scrubland studded with thorns like stilettoes. Eighteen years later he is a bushman as impressive as Crocodile Dundee (though of Rhodesian parentage), a cattle rancher, and a self-educated scholar, whose library ranges from Kipling and Burns to Churchill’s diaries.

He tells us about Paraguay’s struggle since 1989 to recover from 35 years of dictatorship under General Stroessner, how corruption is rife, and how half the country’s budget is spent on the military, leaving little for social security: “once the people could eat but not talk; now they can talk but not eat. ” Three-quarters of the population is of mixed Spanish-Guarani (Indian) heritage, some Indian and 20 per cent are descendants of European immigrants including German Mennonites, who left the Canadian prairies and Ukraine to escape military service (they believe in pacifism, adult baptism and a traditional agricultural life).

The sparsely populated Chaco is such a mecca for birds that student Jamie struggles to include them all in his project. James, our guide, points out a scarce great black savannah hawk, flamingoes, laughing and peregrine falcons, ostrich-like rheas, storks, parakeets, kingfishers, the distinctive red-throated jabiru and the oven bird, which builds a north-facing door in its nest. He also helps another student, Colin, compile information on plants’ medicinal uses for Edinburgh Botanical Gardens and on animals such as vampire and fisherman bats, giant anteaters, tapirs (a relative of the horse) and pumas. “Through James we are gaining insight all the time,” says Jamie.

But not even James is infallible. “It never rains in the Chaco in July, ” he tells us on our way to our first camp site, a beach alongside the remote Laguna Salada. The first drops fall as we unload the truck and the quarter-mile track becomes a quagmire as we transport camp and kitchen equipment, baggage and loads of heavy wooden planks. By the time the tents are up we are ankle-deep in mud and being eaten alive by monstrous mosquitoes. Morale sinks to its lowest when six people fall sick.

We build a wildlife hide here (with the planks), so future visitors will get a 360x view of this fine bird lake. Everyone works hard and spirits rise considerably when the sun finally appears and the sick people recover. First, deep holes are dug for the foundations. Spades soon become redundant and all that can be seen of the smallest team members, Rebecca and Yolima (Fulcrum’s South American representative and translator), are their ankles anchored down by their fellow workers while they burrow down, gouging out mud with their hands. On the third day, all that remains is to affix a Fulcrum plaque with the motto “friendship forever” and declare the hide open. Everyone agrees with John Lowe that: “The fulfilment of this challenge has been really worthwhile. ”

By now the students, who barely knew each other at the outset, have become close and mutually supportive and there is, in Jamie’s words, “a tangible atmosphere of happiness and friendship in the dust-driven cattle truck”. Singing Scottish songs, albeit hesitantly at first, helps to break the ice early on and before long they sing with gusto at every opportunity.

“El Chaco Gringos”, as we now call ourselves, next pitch camp at Ranch San Carlos near Puerto Casado. Some Maskoy Indians have come specially to meet “blonde people” for the first time and show us how they survive in the bush, cook vegetables around a fire deep in the ground, roast an armadillo and eat a cow’s head (which few of us can stomach).

I join a group visiting the huts the Indians live in temporarily while working on the ranches. Through a three-way translation process - Guarani to Spanish to English - we learn their traditional ways are dying out and life expectancy is only 50 years. Eleven adults and three children occupy one tiny hut. “It makes me embarrassed I complained about being cramped three to a tent”, says Ross. “We see poverty on television, but it’s something different seeing it with our own eyes.”

Later, Scottish souvenirs are presented to the eight Indians who led the activities. The headman says they were “all made happy, felt friendship with everyone, and were pleased to be treated with respect, not just for a picture. ” By now, the team’s awareness of eco-tourism issues has heightened, such as the thin line overseas visitors tread between “bringing friendship” and sowing the first seeds of the “baksheesh mentality”, as when they visited the Maskoy Indian village within Puerto Casado. As the village’s first contact with westerners, all went well while students and children played football and volleyball together. But when it came to handing out tools, baby clothes, toys, pens and paper pads, the venturers were upset because they felt the event had developed into a patronising ceremony, prompting women to ask for money and leaving the students feeling uncomfortable with their role.

More successful was a visit to Centro Educativo Maria Medianerade, a school run by volunteer Jesuit missionaries. Funded by the Government and from sponsorship, it is unique in Paraguay since few attend school beyond the age of 12. The 600 pupils aged five to 15 stay for eight months at a time because most homes are a week’s horse-ride away, and they build and maintain everything themselves from Chaco materials. Conventional subjects are taught alongside skills like joinery and dressmaking, which “prepare them for life”. They even butcher their own cattle.

Excitedly, they staged a show of traditional dancing, singing and animal and bird mimicry. The venturers reciprocated with “Oh rose of Scotland” and “I’m climbing up Sunshine Mountain”, handed out gifts and played games with them. The children’s response prompted one student to say: “We take things for granted and they are happy with so little.” The team now plans to send an annual contribution to the school.

Preconceptions about the Mennonite community were also modified: “We heard they lead simple, upstanding lives and don’t swear or drink. They seem friendly, but are brought up to believe Indians are dirty and shouldn’t be at the same table”, said Andy. “And they do drink and swear!” His comments followed dinner at a hotel near the Mennonite colony of Filadelfia, to which two Indians had been invited. They were clearly ill at ease. The students were appalled when James explained that Indians are not normally allowed past the Mennonite front door, have never used cutlery and suffer many hardships.

After these emotional experiences, it was time to relax in Asuncion’s summer resort, San Bernardino, surrounded by hills covered in subtropical vegetation, bright flowers and grapefruit trees; and at Estancia San Carlos where the team rode horses and watched gauchos rounding up and lassoing cattle. The adventure ended with two days’ camping at a Brazilian ranch and heartstopping visits to the awesome Iguazu Falls, of which there are 276 scattered over the Paraguayan, Brazilian and Argentinian borders. We got drenched speeding in rubber rafts to the foot of the falls and watching rainbows chase over them from walkways just spitting distance away.

Fulcrum’s director John Hunt frequently said “an expedition isn’t an expedition until things go wrong”. This trip was no exception, although it was well organised on the whole from provision of vehicles to bottled water and meals. However, most students felt any hitches added realism to the adventure.

El Chaco Gringos were resilient - and needed to be. We had barely touched down, let alone got over jet-lag, before being plunged into a gruelling regime of early mornings, long journeys, hard physical work and meetings. Many worried about finding enough time to complete their projects. The schedule could have been a little less ambitious, perhaps, to allow for the fact that breakdowns are common in remote areas, journeys likely to take longer than anticipated, and that night descends early (many activities such as a specially-arranged steam train ride took place in the dark).

Take, for instance, the day we left Laguna Salada and arrived late at Puerto Casado due to mud, wet tents, and a truck breakdown. Exhausted and ravenous we set up camp in the dark and went straight to meet the Maskoy Indians, who had been awaiting us all day. We stood on jelly legs, incapable of taking anything in, while everything was translated twice. Eventually one venturer keeled over.

How safe were we? During our time in the Chaco, we anticipated unrealised dangers, such as the odd charge from a wild peccary (pig). But hotels? One morning I reached out to switch on the bedside lamp, only to be thrown against the opposite wall - electrical appliances will now feature in Fulcrum’s otherwise thorough risk assessments and emergency procedures. Reassuringly, Fulcrum always has a doctor in the team.

Did Fulcrum achieve its objectives? Undoubtedly. Members of the team enjoyed being “one big happy family”, broadened their horizons and grew visibly in self-confidence and social skills. Ross says he now feels “like a more rounded human being, better equipped to cope with whatever life throws at me” and Jamie says it all with: “I don’t think everything will sink in until I analyse it back home, but I’ve seen more, lived more and endured more than I could have dreamed of.”

* Who goes where? Choosing a challenge with Fulcrum

“Fulcrum wants to find the very best young people and make them even better”, says John Hunt, so participants go through a rigorous selection procedure. The Scottish contingent was interviewed during the autumn term by Young Enterprise Scotland, which gives young people business experience while still in full-time education. Most were managing directors of their own small companies.

Stage two was an activity weekend at St Dounan’s Centre, Aberfoyle, in February, where staff had devised a special programme to give a foretaste of the stamina and team-building skills venturers would need while overseas. Divided into groups, they spent from Friday noon to midnight heavily laden, navigating their way around the forest in heavy rain doing problem-solving exercises. Up again at 6am, they found staff had mysteriously acquired broken limbs and needed carrying back to base on heavy stretchers rigged up with logs and rope.

A mixture of mental challenges and assault course activities followed. Once selected, venturers raise Pounds 800 in sponsorship, arrange a week of director shadowing and do an environmental project - in this case, a weekend at Glencoe repairing footpaths.

Students from all over Britain have joined Fulcrum expeditions to China, East Malaysia, India, Nepal, Botswana and Patagonia.

Further details from: Fulcrum Challenge, Luccombe Business Centre, Milton Abbas, Dorset DT11 OBD. Tel: 01258 881399