"Whoooooohooo!" I can hear the Aberdeen Grammar pupils celebrating as they reach the top of Mount Rungwe, a 2.5 million-year-old volcano which, at nearly 3,000 metres, is the second-highest peak in southern Tanzania.
Unfortunately, I can only see them as distant white specks, thanks to a series of problems, by turns funny and frustrating, which have stopped me accompanying them to the summit today.
My first attempt to meet them last night was aborted after several hours driving around a forest in the growing darkness, when my guide, Nico, eventually confesses apologetically that we are lost and must drive back to the nearest town. For the last mile we are behind a truck with a bumper sticker which reads, appropriately: "Life is Difficult."
After more hours waiting for an official to grant a trekking permit this morning, I've been stalking the Aberdeen team at high speed, setting off almost at running pace under the midday sun in a desperate bid to catch up with them along the trail.
Suddenly Nico gets a call on his mobile from the team, who have just spotted us. To mutual surprise, much helped by the fact that I am carrying far less than the pupils are, I manage to rendezvous with them at the peak, where they are waiting. More cheering breaks out as I finally arrive.
The 17 teenagers, aged 15-18, are one of two teams from the grammar school taking part in a World Challenge school expedition in Tanzania. Like me, they have overcome obstacles to get here, including local roadblocks erected in protest over taxes. These have delayed the start of their hike, too.
Several pupils battled minor illness and injury to make it to the top, and all are understandably delighted to re-enact their arrival for me - posing proudly and holding a Saltire.
Their journey here began back in 2010, when they were first accepted as so-called Challengers - and given the task of raising nearly pound;4,000 each to fund the learning experience.
"I got quite emotional and started crying when we first reached the summit - just because we've been building up to this for nearly two years," grins today's leader, Helen Innes, 18, as she sums up her feelings.
"Being leader is demanding enough anyway, and having to coordinate everyone today was quite stressful, but it was fun, too. The hardest bit was having to think about how everyone else was doing and not just myself."
The group is keeping a team journal, in which Nick Logan recorded his pre- trip hope of avoiding diarrhoea. As we hike down, the unfortunate 18-year- old regularly has to call us all to a halt and vanish into the undergrowth. He remains remarkably cheery, however, fantasising about his first meal back home - pizza and ice cream.
By the time we reach the latest wild camping site, it is dark and we are all tired and hungry. Today's cooking team has a few issues preparing the rice, but eventually dinner is served.
As everyone retreats to their tents for an early night, Nick reflects on his summit experience, saying: "Before I left, I was told (by previous Challengers) that there would be a point when I was so miserable I would want to go home, and it was today, but it only lasted a few hours."
Refreshed after a night's rest, we walk on through vibrant green tea plantations where the Challengers greet curious villagers with friendly calls of "Mambo!" (Swahili for "what's up?")
The expedition lasts four weeks and includes a trek, a community project, a safari and some relaxation time. Each Challenger receives an individual report written by the team's World Challenge expedition leader, Inverness supply teacher Will Snow, which can be used as a reference for Ucas, the university admissions service.
He is impressed by the "very competent and caring" team. "As a teacher, I often feel I'm spoon-feeding pupils, but here we offer experiential learning and they really excel and shine," he says. "They are in a position of responsibility - they have to compromise, endure hardships and learn from their mistakes."
Sitting around the campfire tonight in the darkness, pupils list their personal highs and lows so far and describe what they are gaining from the experience. There is laughter as one teenager's high is the simple joy of "sleeping". Lows include witnessing two Tanzanian children being knocked down by a driver on the country's notoriously dangerous roads.
Nick, who recently learned that he has diabetes, says the expedition has shown him that the diagnosis needn't hold him back.
While this group was starting its trek in the mountains outside Mbeya, pupils in the second Aberdeen Grammar team arrived to do their community project a day's drive away, near the town of Iringa.
I join them as they walk up the dusty track to Kitayawa Primary, where dozens of children in bright blue-and-white uniforms are singing and dancing energetically outside.
Today is a holiday, but these Tanzanian youngsters seem delighted to perform for their overwhelmed visitors, who are soon encouraged to join in. The show becomes a comedy as the Scottish teenagers copy the African moves with mixed success.
There is a serious message, too, as one local schoolgirl delivers a rap with the line: "Education is the key of life - without it where can we go?"
At Kitayawa, about 550 seven- to 14-year-olds are taught by seven teachers in four classes of up to 102 pupils. Tanzanian communities must build schools before the government funds teachers, so if this World Challenge team and later ones complete two new classrooms, Kitayawa will get two extra teachers.
Kitayawa's headteacher Kasian Kalinga explains: "That will reduce class sizes. We are happy to see these people."
Today's leader, Marc Walton, 16, thanks the group of villagers who have come to help. "It's wonderful to see almost a (whole) village community come out and we look forward to working with you. Hopefully, we'll get as much done as possible. Asante sana!" he finishes - the Swahili for "thank you very much".
Next, he discusses supplies and salaries with a local carpenter and a mason, as Richard Phillips, a World Challenge agent based in Tanzania, translates negotiations on spending the team's budget of 1,162,500 Tanzanian shillings (about pound;470).
After the tradesmen list the materials needed, including buckets and cement, Marc leaves to "do some sums".
Managing their money is a key part of the expedition for Challengers who have to buy and cook their own food and arrange transport and accommodation.
The following day several pupils including Andrew Scrimgeour, 17, the team's accountant, visit Iringa to barter for supplies. They haggle with a stallholder over stacks of coloured buckets but he refuses any discount, so they pay the 15,000Sh (pound;6) price for six.
"Our budget was 12,000Sh (almost pound;5) but he wouldn't budge," Andrew says. "He has to make a living, too. We've been saving in just about every aspect, though, so far."
Back at Kitayawa, Fraser Mackintosh, 16, is leading a singalong of My Bonny Lies over the Ocean as pupils from Africa and Scotland pass bricks to the mason for the floor of a part-built classroom.
Making concrete is tough, as 15-year-old Claire Henderson discovers, wielding a spade in the heat. "It's hard work, but it's a really good experience," she says.
As villagers flick the mixture expertly on to walls, there is frustration among the Challengers that they themselves cannot do more. Some, including Becca Fennell, 18, start freshening up existing classrooms, painting African elephants and a large sun on one wall.
"It's so strange to be here," she says. "Stuff like this is like what you see on TV. It makes you appreciate what you have."
At evening briefings, the team's World Challenge expedition leader, Henry Litchfield, teases out issues using techniques like the "rose and thorns", where pupils hand an imaginary flower to someone who has done well, and give themselves a thorn for something they could have done better.
Meanwhile, maths teacher Ryan Robertson and head of English Lynsey Struthers talk to pupils to check they are coping with homesickness, stomach upsets and culture shock.
Back in Iringa, pupils buying supplies, including today's lunch, worry that those back at Kitayawa may be hungry, as they wait to change money at the bank as there isn't enough currency in stock.
When we finally reach the food market, Cameron Howe, 17, - the self- appointed team "chef" - grins and haggles with ease. His most inspired purchase, however, is an impulse buy from the Hasty Tasty takeaway where he snaps up a whole swiss roll for 8,000Sh (pound;3.25) as a treat.
"They can't be annoyed now," he says gleefully, as we return to the school. And he's right.
`YOU HAVE TO BE ABLE TO SWITCH OFF FROM TEACHER MODE'
"I was very much a `luxury holiday, week in the sun' person, but I love this now." Alan Martin, depute head at Aberdeen Grammar, readily admits that roughing it in the jungle with a group of teenagers didn't appeal to him at all, until he tried it.
Now on his third trip with school expedition company World Challenge, however, he is a firm convert.
"The rewards outweigh the worries and fears you have beforehand and you probably think it's more difficult than it is," he says. "I think every teacher should think about (doing) it, for their own personal and professional development.
"You do have to be a certain character, though. You have to be able to switch off from teacher mode and become a Challenger as well, and you have to be prepared to not be shocked by things. The pupils become very open about everything!" - a reference to regular banter about bodily functions inspired by the sometimes unpleasant side effects of travelling.
The school's latest World Challenge experience is this four-week expedition to Tanzania for two teams of 17 pupils apiece. Each team has a World Challenge expedition leader and two teachers to meet the company's standard ratio of one adult to eight pupils, and World Challenge pays for first-aid training for its staff and teachers.
Emergency back-up measures include a satellite distress beacon and a satellite phone, and all activities are risk-assessed before the expedition. The teachers' main role during the trip is pastoral.
Pre-trip administration doesn't take too long, says Mr Martin, as most forms are online and World Challenge provides "really good" support.
Photo: Aberdeen Grammar pupils help to decorate classrooms at Kitayawa Primary. Photo credit: Julia Horton.