For weeks, Stephen Bishop came to school straight from sleeping rough.
Dirty and dishevelled, he faced a class of 53 children in a school with no telephone and no running water. But nobody really minded that he had spent the night in a field, or that his clothes could do with a good wash. They were just glad to have a teacher - any teacher - and hope that the lessons would one day help to free them from poverty.
And Stephen? He has had the time of his life as a deputy expedition leader with Raleigh International. Brought up in Bristol, he joined the Royal Army Ordnance Corps after leaving school, serving for four years as an army photographer. Then, after a period working with the Ministry of Defence, he took a degree at Bath University and qualified as a teacher.
But after teaching for almost six years, specialising in geography, he felt the time had come to broaden his experience and, in particular, to see at first hand a few of the things he had been describing in the classroom. "I wanted to see things and work in a developing country," he explains, "and to experience some of the physical features, such as volcanoes and rainforests, that I had spent so much time teaching people about, but had never actually seen.
"I also wanted to improve my skills base - to improve my Spanish, for instance, and to practise new teaching methods."
So, at the end of last year, Stephen, 36, left John Bentley secondary school in Calne, Wiltshire, where he had taught humanities for two years, and in January flew to Nicaragua for a three-month stint as a volunteer worker with the youth development charity Raleigh International.
There he trained younger volunteers (aged between 17 and 25), and was involved with several projects, including the construction of a central boarding school for students unable to travel every day from their far-flung communities. But his main responsibility was teaching English in a scattered rural settlement that straddles the inter-Americana Highway some six kilometres south of the city of Granada.
"There are four primary schools and one secondary school, mostly antiquated two-room buildings with as many as 53 children in each class," he told me last month as he prepared to leave Nicaragua. "There is a huge teacher shortage, so by teaching maths, geography and English, the Raleigh project is taking the pressure off the local teachers and also adding a little cultural awareness to the curriculum."
Stephen taught English to the children, and provided teacher training for the other Raleigh volunteers. When he wasn't in the classroom, he was exploring the local terrain.
"A party of us did a five-hour climb to the top of Mombacha, a volcano at the foot of Lake Nicaragua. It was a real first for me. Mombacho hasn't erupted for 400 years, but there was plenty of steam and a horrendous smell of sulphur."
The weather was dry enough for the school-based volunteers to sleep outdoors in the field where they set up camp. They lived on dried food - pasta, rice and beans - which they took turns to cook, supplementing it with local produce. And they became, Stephen says, "absolutely filthy, and not a very good example to the children". But the community and the schools welcomed them with open arms.
"They are very, very nice people, but very poor," says Stephen. "There are maybe 2,000 living there, but only one telephone. The pump has broken and they can't afford to have it mended, so there is no running water either.
But the children are keen to learn, and they see education as a way out of the poverty cycle."
Stephen is now travelling in Central America, taking in some rainforest trekking and climbing the most famous volcano in Costa Rica, the still-smoking Mt Irazu. Then it's back to England in time to find a new teaching job for the winter.
This time, he says, he will be taking a wealth of valuable experience into the classroom with him, as well as enough photographs to bring any geography lesson to life. "I can really recommend Raleigh as a career break for any teacher," he says, "and especially for anyone teaching geography.
"Volunteers have to find their own air fares, and the whole thing cost me pound;750, with the same again coming from local firms' sponsorship and from family and friends. But we all believe that's how it should be, because we gain so much from it in terms of personal development."
For more information, visit www.raleigh.org.uk