Toul Sleng high school in Phnom Penh hasn’t been a school for more than 30 years. But it teaches a history lesson as compelling as any in the world.

When the Khmer Rouge came to power in Cambodia in 1975, their vision was for a communist society in which every man, woman and child would work the fields. Education was the greatest threat to that vision, so schools were closed and teachers persecuted. Toul Sleng became a brutal detention centre for thousands of educated Cambodians: doctors, government officials, but particularly teachers.

Those suspected of being educators, often because they wore glasses or had soft hands, were sent here and tortured until they “confessed”. Then they were shot. Today the school is a genocide museum and tourists queue to see cabinets packed with skulls instead of textbooks, classrooms converted into cells, and playground climbing frames transformed into instruments of torture.

A quarter of a century after being overthrown by a Vietnamese invasion, the Khmer Rouge still casts a shadow over many aspects of Cambodian life. And none more so than its education system. When the regime collapsed, teaching materials had been destroyed, school buildings razed, and an estimated three-quarters of the teaching profession killed. Those who survived were reluctant to return to the classroom for fear that the party, which remained active until the mid-1990s, might one day regain power.

“The Khmer Rouge ripped the spine out of schooling in this country,” says Iv Sarik, who has devoted himself to education as a way of making amends for his earlier life as a Khmer Rouge supporter. Recently retired as deputy director of education in the Takeo province, he now works as a translator.

“We’ve come a long way. We have a young, willing workforce, and some good school buildings. What we lack is experienced teachers, and the skills that experience brings.”

This is where Voluntary Service Overseas (VSO) comes in. Since its foundation in 1958, VSO has been sending teachers to classrooms across the developing world, but in Cambodia, and in other countries, it is now recruiting “education managers” rather than classroom practitioners.

Operating at a more senior level, these volunteers train teachers and trainers, and prepare resources that will be of value long after their two-year placement has ended. Twenty-four such people are needed to start work in Cambodia this September; numbers may have risen to 70 by 2010.

After six years as headteacher at an independent girls’ school in Lincolnshire, Pat Clarke had exactly the experience and skills VSO was looking for. And at 57 she was ready for a new challenge. “I’d been worn down by constant 14-hour days,” she says. “I could have held out for early retirement, but there’s more to life than money. Education changed everything for me. Going to university allowed me to do things that no one in my family had been able to do before. Without wishing to sound like a saint, I just wanted to give something back.”

VSO was something she’d been “mulling over”, but she had reservations. One was that she didn’t like “roughing it”. Sitting on the balcony of her beautiful wooden house in the riverside town of Kompong Cham, with the fan whirring soothingly overhead, she admits she needn’t have worried. While VSO teachers in Africa sometimes live in basic accommodation, volunteers in Cambodia discover their monthly allowance of around $350 (pound;182) buys a comfortable, spacious home, often complete with domestic help.

Having devoted much of her working life to girls’ education, Pat also wanted to avoid volunteering in a Muslim country. “I’d have become a suffragette,” she laughs. Predominantly Buddhist, Cambodia offers girls, in theory, the same access to education as boys. But while at primary level numbers are roughly equal, at secondary school the proportion of girls dips sharply. Currently, things are worse than usual. Last year’s monsoons arrived late and the rice harvest was poor. In these circumstances it’s the girls who suffer. In poor families they are kept at home, to work or look after children. In desperate families they are sold by their parents; sometimes, particularly on the border with Thailand, into prostitution, or, more often, into the restaurant trade. Increasingly, girls from the provinces are also drawn to the capital in the hope of finding work in textile factories serving the big western fashion chains. When they get there they have nowhere to stay and no money, making them easy targets for exploitation.

The scheme Pat Clarke administers is simple enough. It helps the poorest families to send their daughters to school by offering a basic grant of a bicycle. In some cases the scholarship extends to money for clothes and food, and even covers boarding if the distances make daily travel impossible.

“It’s important to show girls that there’s an alternative to early marriage. Having an education will help them when they face difficult decisions in their life,” says Pat Clarke.

She knows all about tricky decision-making, having left her partner behind in the UK to come to Cambodia. The first thing she told him when they met up a year later was that it had been worth it. “I’ve missed him, but I’ve achieved something of real value, which makes the sacrifice worthwhile.”

Peter and Margaret Harvey, VSO volunteers working in Takeo, south-west of Phnom Penh, dub Pat Clarke a “tough cookie” for coming to Cambodia alone.

They applied to VSO as a couple. Margaret had just taken early retirement from her job as a primary teacher in Bristol, while husband Peter was working for the Learning and Skills Council, having already clocked up 17 years as a secondary deputy head. “Early retirement sounds nice, but actually it can be a bit depressing,” says Margaret. “You wonder if your life is ever going to be as valuable as it has been in the past. This way we’re doing something that’s even more valuable.” They were fortunate to find placements in the same area, doing similar work. “Being together helps us enormously. We can let off steam, talk things through with each other.”

Her husband is based at the regional teacher training college (RTTC) for secondary teachers, where he monitors training and has introduced the kind of basic professional development that is still unusual in Cambodia, such as organising workshops that bring together NQTs and teachers from across the province to hone skills and share ideas.

Peter Harvey’s tour of the RTTC begins among the pigs and chickens in the grounds. We enter through the side gate; the college has become a popular short cut for petrol smugglers and the main entrance has been closed by police. Many of the 400 trainee teachers are only 18. Sitting in uniforms behind regimented desks they look, and are treated, like schoolchildren.

When we enter the room they stand up. At the beginning of the day the director talks to them for more than two hours at the daily assembly. At the end of classes, they retire to dormitories, each with around 20 beds jammed in rooms seven metres square, and no electricity. It’s not long since the government paid trainee teachers in rice (and wood to cook it with). Now they receive just over $2 a month, which amounts to roughly the same thing.

Yet such is the level of poverty that there is no shortage of people wanting to become teachers in Cambodia; around 10 applicants for every post. But getting quality recruits is not so easy. A qualified teacher earns around $35 a month, barely enough to clothe and feed a family; a taxi driver in Phnom Penh might make six times that amount. As a result, most teachers have second jobs, usually back-breaking work in the paddy fields.

Unsurprisingly, Peter and Margaret Harvey find it difficult to be as demanding as they would like. “How can we reasonably ask people to work through new materials after school if they have to work to feed their family?” says Peter Harvey.

Based at the provincial office for education, overlooking the Takeo lake where she jogs every morning, Margaret Harvey helps government officials to train primary teachers. The overall aim is to replace the formality and rigidity in schools, which still resemble the British education system of 50 years ago, with a more learner-centred, child-friendly environment. A short drive away, at Angtasom primary, only the lines of children at the 7am flag ceremony hark back to old methods. The rest of the morning’s lessons are creative, energetic and interactive. There are outdoor games, storytelling and traditional dance classes, and children work on their own in small groups scattered around the school. “This is good,” smiles Margaret Harvey. “Very good. But, unfortunately, in a lot of schools it won’t be like this.”

Part of the problem is class sizes; 60 is not uncommon. At nearby Chea Sim high school, for example, there are more than 4,000 students. A shift system of either mornings or afternoons means children effectively spend only three days a week in school. And overcrowding is likely to get worse in the government’s push for “education for all” by 2015. Currently, 90 per cent of children go to school, though many only attend for a few years.

“These statistics are not everything,” says Nath Bunroeun, under-secretary of state for education. “What matters is the quality of education children receive. The quality of teaching must improve, especially for English and computing. These are the skills that will transform Cambodia.” Many schools have ICT and science equipment that sits gathering dust because no one knows what to do with it; a stark example of how developing countries need more than just material aid. English is taught in secondaries, but often by teachers who speak no English themselves.

Clearly, this is an area where VSO volunteers can provide advice and develop resources, but first they have to get a grasp of the Khmer language, which they all agree is a mighty challenge. Pat Clarke can chatter away in French, German, Russian and Italian. “But this is different,” she says. “As languages go, Khmer is a stonker.” Margaret and Peter Harvey work with translators, though even that brings frustrations.

“Sometimes I want to teach a model lesson, but by the time it’s gone through a translator you’ve lost all spontaneity,” sighs Margaret.

Another challenge is getting from A to B. Or at least getting there safely.

The most common form of transport is the 125cc motorcycle, which in Cambodia frequently accommodates five or more passengers, plus live chickens on the handlebars or a precarious trailer full of pineapples. With no apparent highway code, crossing the road on foot is daunting enough, let alone trying to negotiate a roundabout on an unfamiliar motorbike. VSO arranges motorcycle training in the UK before volunteers depart, and then provides the “moto” and helmet when they get to Cambodia. Even so, just days after her arrival, Margaret Harvey hit one of the countless potholes and broke her arm in five places. An unfortunate start, but at least it showed her the level of support volunteers get from VSO. “A doctor accompanied me to Bangkok hospital,” she says. “Everything was covered by the VSO medical insurance, and I’ve been having physio every week. The back-up couldn’t have been better.”

The crumbling roads make life hard for the education managers who work across a wide area and need resourcefulness and patience. Pat Harvey recently endured a 13-hour journey to a school 200 kilometres away.

Squeezed into the back of a truck, she was the only woman, with no chance to go to the toilet.

Despite such trials of stamina, she is convinced that older volunteers have most to offer VSO, which from September plans a major expansion of its Cambodian programme. “After 30 years in education there’s not much you haven’t faced. You have mental and emotional resilience.”

James Whitehead, VSO’s programme director in Cambodia, says he would consider thirty-somethings, with experience of running a department, as potential education managers. But Pat Clarke would like to see more “golden oldies” applying. “You’re trying to change attitudes, and that’s never easy. I’m not sure a younger person could do it. At my age, I have nothing to prove. I’m here because I want to enrich the lives of others, and in doing so I’ve been lucky enough to enrich my own life. You grow as a person, at a time when you think you’ve stopped growing.”

How do I volunteer?

VSO is recruiting 24 education managers to begin work in Cambodia from September this year. Around the world there are 59 other such placements for senior educators - in Ethiopia, Ghana, Uganda, Namibia, Nepal, Nigeria and Vietnam.

* Most contracts are for two years, although there are some one year placements for primary teachers. There is a guarantee of at least three weeks’ holiday a year.

* Volunteers receive a living allowance, accommodation, and return flights as well as medical and travel insurance. They also receive a grant (usually around pound;1,500 if they’ve done a two-year stint) on completion of their contract.

* VSO makes NI contributions on volunteers’ behalf, and offers some compensation if it isn’t possible to make pension payments.

* VSO provides seven to16 days’ training before departure, as well as a comprehensive induction programme, including language tuition, on arrival.

* Anyone thinking of applying for September should register an interest as soon as possible. Interviews and assessment days are ongoing and are held in London.

* Seventy-five per cent of people invited for an assessment day are offered a placement.

* VSO accepts volunteers up to the age of 75.

* More information on the application and selection procedure can be found on the VSO website. Application forms can be downloaded online www.vso.org.uk.