What kind of holiday is it when you pitch your tent outside a school? On the safari I went on in East Africa, a day and a night at a primary school in Kenya are an essential part of the 17-day trip.

Our truck, “Claudia” - a specially built supermodel, albeit one with the chassis of a cement-mixer - pulls up outside Kariandusi primary in the early afternoon, after a 90km drive from Nairobi on the spine-shattering Rift Valley highway. Colonel Harrison Vialou Clark (“VC”), chief mover and shaker of the charity that helped build the school, welcomes us. We sit on rough benches in the old school, half-blinded by the shafts of sunlight that pierce the cracks in the crumbling mud walls, our feet finding sharp rocks in the thick dust.

The old site is a typical harambee (“pulling together”) school, built by the local community, as are most primary schools in Kenya.

On January 16, 2003, VC tells us, the new president of Kenya, Mwai Kibaki, declared that all children should have free primary education and no child should be turned away from school. A hundred new children arrived at Kariandusi the next day. “It was pandemonium for three months,” he says.

“Heads were tearing their hair out.” They weren’t expecting the announcement and there was no state provision for it. But they needed a new school.

It took a year and 15 days to complete the new school. “On February 14, 2005, a date carefully chosen by me - one of love - we had a great rejoicing,” says VC.

As part of the tour operator Dragoman Overland’s “responsible tourism” ethos, I and my 12 travelling companions are soon helping out at the school: unpacking books to fill the shelves of the new library, sanding down blackboards, and painting walls. Kariandusi has 384 pupils. The largest class has 66 children in it, the smallest 35. Teachers are in short supply. “Most parents are farmers,” says headteacher Samwel NdungNo. “This is a very dry place. They are poor. Most children don’t have lunch, then they cannot learn.” Despite the difficulties, he says, “we are able to sustain 90 per cent attendance”.

Mr NdungNo cannot remember the last time there was a good harvest locally, although the Kariandusi area has not suffered the extremes of drought and famine seen in the north of the country.

The government has put some money into schools since its groundbreaking announcement in 2003. Children get a textbook allowance, for example, but local communities are still responsible for building their own primary schools. And schools do not come cheap: Kariandusi cost pound;45,000 to build - a modest sum by British standards, but a staggering sum for a community project funded entirely by donations. As well as providing volunteer workers, Dragoman Overland contributed more than pound;5,000. It is, the company says, a “great example of how tourism and grassroots charities can work together”.

At another of VC’s projects, the nearby Langalanga primary school, the head Patrick Ichoho tells a similar story. “We have many children who are hungry. They have only one meal a day, and that is not a good one.

Breakfast, if they have it, is a cup of tea with no milk.” At Langalanga, as at Kariandusi, there is no electricity, although Mr Ichoho hopes to install it one day. That would enable the school to run evening adult education classes, for which there is a huge demand.

Back at Kariandusi, Dragoman travellers chat to Mercy Mbaya, an English teacher, and some of her pupils. Other children and teachers join in as lessons end for the day. The children’s cheeriness is infectious.

After the afternoon’s work many of us are splattered with paint. But everyone agrees with Australian office worker Shiralee Gillies: “It was definitely worth it.”

Mercy Mbaya invites us home for dinner and a shower, but we politely decline as we have other plans. First, we pitch our tents on the bald hillside between the new school and the old. The wind blows them away and whips the gritty dust into our faces. There is no running water and one long-drop latrine.

After a quick scrub-up with a fistful of Wet Wipes we walk down through the village to Lake Elmenteita, where the wind whips the soda shore into white clouds and flamingos and pelicans gather. Everywhere children run out to see the strange painted visitors. We are invited into family compounds and attempt to communicate. At an orphanage, we are given dinner: ugali (cornmeal), beef stew, cabbage and beans.

It’s hard to sleep on the hill: we keep rolling out of our tents, the trucks on the highway roll noisily through the night, the wind never drops and several times I hear one of my fellow travellers hoicking like a hippo outside his tent. This, the unlucky 13th of our group, who became sick on day one of the trip, continues to feel so ill that he later cuts short his holiday. We had been warned. “You need to take responsibility for your own health and happiness on this trip,” our Aussie tour leader, Adam, had told us.

Next morning, pupils begin to arrive at 7am, an hour early for school. Mr Ndungu calls the pupils out to the front of the school to say goodbye to the visitors. They’re encouraged to wriggle and wave their hands to warm up for the big round of applause that is their thank you to us. We try shake as many hands as we can as we say goodbye.

Later in the trip, on the ferry returning from a sybaritic stay on the beaches of Zanzibar, I meet a Tanzanian active in promoting exchanges with Britain. He has no illusions about how little difference individual travellers can make. But he wants people to keep on coming, “because you are the ones that receive an education. Then you can go home and explain who we are - people just like you.”

More information: www.kariandusi.co.uk. The opening ceremony of Langalanga primary school is on September 15 and the ground-breaking ceremony of the next project, Simba primary school for 800 pupils, is on September 9