there used to be a postal sorting office at Dumfries train station, but it’s a long time since parcels arrived with a thump and letters click-clacked into mail racks. These days, the noise has been replaced by a scarcely audible thrum of scholarly endeavour.

The modest building is home to the River of Life Christian School, where pupils aged 5 to 18 sit quietly in a network of booths and work through a vast pile of booklets throughout their school days.

Standard grade and Higher are unfamiliar terms here. Individualised learning with a religious thread is preferred, built around the American Accelerated Christian Education system. Testing goes on throughout each child’s time at school, but there is no build-up to pivotal exams at a pre-determined age. Staff liken ACE to the International Baccaleaureate.

Although there is a handful of other independent Christian schools in Scotland, only one (Living Water in Bellshill, Strathclyde) uses the same system, and it has no secondary pupils.

The school’s 24 pupils spend much of the time isolated from each other in individual booths, going at their own pace, setting themselves weekly targets and marking their own work. The booklets are divided by subject and the pupils decide which ones they should be tackling each day. A timetable with periods for set subjects only applies in the afternoons, for the likes of art and PE.

Most pupils are usually found in the same open-plan room, although two infants which children are deemed to be until they can read spend a lot of time in a smaller room with booths, a play area and toys.

If a child needs help, he or she attaches one of two small flags to the top of his or her booth the international Christian flag for bigger problems, the Union flag for less pressing needs.

The conditions make for a quietness that pervades the school. The teachers speak softly, gently encouraging pupils, while the head, Helen Smith, keeps an eye on things from a raised stage in the room, where she often works.

The quiet diligence can border on the monastic. Even at lunch time, there is a conspicuous lack of boisterousness inside. The dining table is orderly and after meals the older pupils find corners where they gently pluck at unplugged electric guitars or update personal networking websites.

The exception is the lively playground, which could be at any school. This provides an outlet for creativity and play, where the supervising teacher can expect to be the butt of good-natured banter.

Matthew Fisher, 15, has friends at nearby state schools but is not sure that he could cope with the bustle there. “If I was in a big room full of desks, I wouldn’t get so much done,” he says.

Sean Ocansey, 10, has mixed feelings about the booths. “People can’t really disturb you,” he agrees, but “sometimes it feels tight”.

Perhaps the school is too quiet. An HM Inspectorate of Education report in 2003 identified a lack of opportunities for direct, active learning. The staff have since introduced more group work, including practical maths sessions, but pupils remain a little timid when learning among peers.

Matthew’s sister Naomi, 13, confirms there is more opportunity for working in groups now but says it tends to be in subjects such as home economics and PE.

The HMIE report found the constraints of the programmes and learning activities often did not enable pupils to achieve their full potential. The follow-up report in 2005 recognised that staff had acted on this by, for example, questioning pupils to check they had understood work.

There are signs, too, of creativity on the walls. One display depicts “Scottish heroes” such as Robert the Bruce, John Knox, Mary Slessor, the Rev Henry Duncan, Robert Louis Stevenson and Alexander Fleming, but the displays are not as abundant or vibrant as in many schools.

The largely solitary style of learning may be out of step with current trends in education, but staff point to the success of past pupils. Several have gone on to higher education, including Aberdeen, Glasgow and Cambridge universities.

While admissions officers are often unfamiliar with ACE, Mrs Smith says no pupil has ever lost a place for the lack of Highers. Indeed, many of them adapt to university better than other students since they are used to working on their own and ACE’s flexibility allows the more able to cover university level work.

Former pupils have also gone into the media, the Royal Air Force and football coaching. One set up an English-translation business in Kabul after the fall of the Taliban.

School inspectors were unstinting in their praise for the rapport between pupils and staff, perhaps unsurprisingly given the school’s origins in home tutoring.

Mrs Smith and her husband, Mark, the school’s administrative principal and a teacher, took their two eldest children out of P1 and P3 at a local school in 1991. They were later asked to teach another family’s children, and when demand increased they were persuaded to open the school in 1994.

The staff includes six teachers and an administration assistant. Only one, David Rudd, is a qualified teacher, having taught history in England for about 20 years, although others have worked in schools and youth groups. A small number of people with expertise in areas such as science and business come in less frequently to teach, one of whom is a Scottish-qualified primary teacher.

The staff’s commitment is impressive. Some are qualified to earn a good living in other careers, but all get by on little more than the minimum wage while performing various duties. Sometimes older pupils help out, for example, filling in forms for a supermarket schools voucher programme.

School resources are poor. The 2005 HMIE report noted that some ACE booklets were outdated, with obsolete measures of volume in maths and European maps from the early 1990s. They can also be frustratingly US-centric: one boy says he knows a lot of American history but would like to learn more about the past closer to home. The lack of a science lab means dissection has to be studied through videos.

Staff would like to move into a bigger building and purchase more books and equipment, but they do not want fees (up to pound;180 a month) to be prohibitive.

The school is an offshoot of the Dumfries-based River of Life church. On Sundays the main room is cleared for the 100-strong congregation to worship. It is part of an international movement, that emerged in the 1980s, of people who wanted to form churches more active in everyday life. It is affiliated to the Evangelical Alliance, a UK umbrella group.

Not all pupils are members of the church, or even practising Christians. Parents choose the school because of its faith-based values and the opportunity to learn at one’s own pace, says Mr Smith.

The prospectus states: “We bring God into every area of the curriculum... Genuine Christianity is about everyday life attitudes, decisions, behaviour and, of course, beliefs.”

Posters with biblical messages punctuate the walls and each ACE worksheet carries a passage from the Bible, that pupils are asked to think about. But Mr Smith believes it would be over the top to have a biblical message crowbarred into every piece of work. Instead, he wants to concentrate on the “big picture”, nurturing values such as tolerance and understanding.

“I like this school because it’s a Christian school,” says 10-year-old Sean. “It teaches you to be a better Christian. You have to show that you’re Christian and not just as if you’re a normal person. I have to be friendly and stuff.”

Teachers try to expose pupils to a range of beliefs and opinions, including lessons on other religions. “We don’t seek to indoctrinate; we want them to investigate their own faith,” says Mr Smith. “There is no way we would impose views upon them.”

Inherent biases can emerge, however. Matthew, an intelligent and independent minded boy, says he has learnt about creationism and evolution in almost equal measure, but adds: “It’s kind of one-sided in favour of creationism.” He says he would like to find out more about evolution.

Mr Smith, whose beliefs tend towards a literal interpretation of the Bible’s message, emphasises that staff are scrupulous about presenting all sides of an argument. He overhears Matthew in passing and is surprised, but says he will look at putting more emphasis on evolution when the origins of humankind are taught.

Homosexuality is also a thorny issue, but the guiding principle taken from the Bible is that no person is superior to any other. Although Mr and Mrs Smith believe a gay lifestyle is not condoned in the Bible, their two eldest children who share their religious beliefs have gay friends in London. The couple compare this to being friends with someone who has sharply differing political views.

Sex education is covered in less detail than in state schools, with the biology of sex taking up a single afternoon lesson a year. In religious and moral education, teachers recommend no sex before marriage, but the children are told not everyone shares that view, says Mr Smith.

Some River of Life methods will raise eyebrows, but the school’s pupils prove it does some things very well. They are polite and caring, older children often spend spare time playing with younger ones, and bullying and indiscipline are almost non-existent. Some pupils are introspective, others engagingly cheeky. Creativity and intellectual discussion may appear muted, but senior pupils are eloquent and contemplative, aware of the school’s religious basis while open to other ideas.

Many will see the school’s booths as divisive and the reliance on biblical values as inculcation. Staff believe the booths are liberating and that biblical values provide a moral template. What is certain is that River of Life’s pupils are not scripture-quoting clones. Perhaps they are quieter, perhaps better behaved but, all in all, they are not so different from children in any other school.