A physics practical involving glass blocks, wooden boards and handfuls of small, sharp pins is a lesson many teachers would dread.
But not a single pin goes astray in Simon Fairway's grade 12 physics class, where the pupils are attentive, polite, respectful, hard-working and wear immaculately pressed uniforms. Several of them are also considerably older than their 21-year-old teacher - and in some cases are married with children.
"The school probably has 20 or 30 students who are older than me," says Mr Fairway, a maths and physics graduate from Kettering, Northamptonshire, who is spending two years as a volunteer teacher at Soltech school in Solwezi, a town in Zambia's remote north-western province. The students' age profile is just one unfamiliar feature of working with Voluntary Service Overseas in developing countries.
Many of the 600 VSO teachers operating in 40 countries are teacher trainers or work in government offices, helping to develop policy, and developing their own skills in the process. More than two in three volunteers are trained or experienced teachers who have given up jobs to experience a very different way of life; as a graduate sent abroad with a week's classroom training, Simon Fairway is in the minority. But whether new or experienced, none of the volunteers do it for the money; they get an "allowance" equivalent to the local salary plus free accommodation, which can make them comfortable by local standards. (Keeley Wilson, a colleague of Mr Fairway's at Soltech school, says she has never had so much disposable income in her life.) Motives vary, but reasons given by VSO's 10 north-west Zambian volunteers include a desire to live and work abroad, to do something useful, to try teaching, to take time out after university and to escape stressful or dead-end jobs in the UK. Altruism can be its own reward, too. "Teachers often regain their passion for the job after a couple of years abroad, and stay in the profession longer as a result," says Katrina Nevin-Ridley of the VSO. "They often get promoted fast when they return, because they have had to be adaptable and often had a lot of responsibility. Some heads tell us they will always call former volunteers for interview."
Research published last summer by London University's Institute of Education suggested that teacher sabbaticals can dramatically improve teacher commitment, motivation and - importantly - retention. The strongest effects were found in beginning and mid-career teachers. Researcher Dr Elaine Unterhalter says: "Teachers bring back qualities that enhance their work - breadth of understanding, team working, commitment to children's learning - and give them new enthusiasm for the profession."
Teaching in a Zambian school is not an easy option. Textbooks are scarce; government funding arrives so infrequently and haphazardly that headteachers spend much of their time placating electricity and telephone companies and trying to source food for their boarders on the cheap; and health problems such as the region's Aids pandemic mean local teachers can be absent for days nursing sick relatives or attending funerals. Yet the volunteers clearly love the life. They enjoy the local culture, the chance to take on more responsibility, and a different approach to teaching and learning.
Anne Sherlock, 25, who previously taught maths for two years in Pitsea, Essex, says: "It's been nice to go in and just teach a class without having to do all the classroom management part of things. When I was teaching in the UK, I would always have to spend the first 10 or 15 minutes getting the class settled, and come up with new ideas to motivate them using laptops or graphic calculators. Here, you greet the class, they are friendly and reasonable. It was a big change at the time. I will miss it. Having said that, they can be lethargic."
For Anne, unusually the only trained teacher among the volunteers in north-western Zambia, there were many differences in school management to understand. "I feel more settled now," she says. "It's very different. People are more open in the UK; here you have to ask a lot more questions. At school in the UK, there is a lot more back-up from senior management - incentives, sanctions; here, you're on your own. But there's much less paperwork."
VSO teachers in Zambian schools have the opportunity to take on all sorts of responsibilities and projects that would not come their way in the UK. According to Mark Hinsley, a former environment engineer now teaching at Kasempa boys' boarding school six hours into the bush from Solwezi, learning to say "no" is a useful strategy. "There just aren't enough hours in the day. You could give yourself a nervous breakdown," he says, pointing at the stinking, derelict washblock the volunteers want to replace. "School administrators tend to load you with as many jobs as they can, and when you're new, you do it. There's also a tendency to think white people must be experts. We're trying to encourage Zambian colleagues to do more."
The chance to live in another culture is important to the volunteers. "When we first got here, two or three people a night would come round to visit us. It was a bit exhausting, but we didn't want to be rude," recalls Anne Sherlock.
Mark Hinsley says: "Some things here are better than in the UK. People have a lot more time for each other, and are a lot more open and friendly. They always greet each other in the street. But being on time is not important here; you turn up for a meeting and it's half an hour before it begins. School sports day started two-and-a-half hours late because the education official who was coming was late and people here show great respect for those in authority."
Simon Fairway adds: "There's no bullshit here. People have more important things to worry about."
The volunteers believe the experience has made them more resourceful and adaptable, and will be useful when they return to the UK. Most of the untrained teachers would now seriously consider doing a PGCE - except Simon Fairway: "It's been great, but do I want to be a teacher? No." Keeley Wilson, who has a master's in environmental conservation, wants to stay in Zambia as a teacher. "My mum says I'm happier than I've ever been."
Anne Sherlock, who returns to Scotland this month, says: "When I go back, I will be more appreciative of the resources I have. I don't have basic books, papers or anything. When I think how much I used to waste as a teacher at home... The same goes personally. I will be more appreciative of what I have and what other people have.
"It's good for a teacher to come somewhere and talk to a different group of people. It helps you find other ways to explain things. I'm thinking a little bit faster."
A VSO leave of absence pack for teachers is due out in the spring. To find out about the latest placements, contact the VSO enquiries unit, tel: 020 8780 7500; www.vso.org.uk