The fourth set of steel-reinforced doors clangs shut behind me after I satisfy the identity checks. Outside, the Carlford unit is a bleak, barbed-wire fortress, unfriendly and seemingly impregnable - one of the most secure prisons in the country. Inside there is a welcoming atmosphere as prisoners and officers greet you warmly.

Carlford, in Suffolk, houses some of the most dangerous young criminals in the UK: 30 young men aged between 15 and 18 found guilty of murder, violent assault, rape or other sex offences. Many of them face life sentences, a daunting prospect for people so young.

Today is family day, one of four held every year to encourage relatives to visit communally, watch a demonstration of work that the group has prepared, celebrate their successes, enjoy a buffet and spend family time in free association between cells and corridors.

I had expected the mood to be heavy, laden with resentment for wasted lives, with occasional outbreaks of jealousy. Instead, I enter a world of positive reinforcement, albeit with a strong emphasis on education and achievement.

Officers address inmates by their first names, readily discuss their activities, take privileged prisoners out on Duke of Edinburgh award projects and sit in on lessons to cover the same work expected of these young men.

In the informal setting of family day, certain tensions might be expected, but the prisoners are well behaved although there is some anxiety in the air because the trains from London to Suffolk have been delayed. However, soon mothers and fathers, brothers and sisters, girlfriends and babies are being warmly greeted.

The officers and education team here value family contact because it enables them to communicate what they are trying to achieve with the boys. That way, any progress stands a better chance of being sustained when prisoners eventually return to the community.

“Relationships and commitment are the key to making this place work,” says Steve Garner, a senior officer and the man in charge today. “Our staff work incredibly hard, but what is rewarding is that the boys respond.”

Education was the watchword when Carlford was set up nearly three years ago inside Warren Hill prison at Hollesley Bay, about 15 miles from Ipswich.

“We have to make the lads accept responsibility for their behaviour,” says Mr Garner. “They have to understand that education is one of the major routes to changing their lives.”

The logo on the officers’ T-shirts reads: “Developing Positive Choices”, and that spirit is reflected in the way the inmates here are treated. Staff are carefully selected to find those ready to support a regime of rewards and reinforcement. The officers worked with a psychologist to design a daily routine that would help to rescue such damaged lives.

The building, a converted hospital, is not ideal, but it is bright and well lit. The inmates can personalise their cells with posters and have their own keys, overridden by master keys when they are locked up at lunchtime and at night, so that they can keep their possessions safe.

The inmates have 30 hours of lessons per week, studying mainly mainstream subjects for GCSE and AS-level. This year, there were 58 passes around the unit.

One teenager who arrived only a year ago managed six A-C passes. He worked so hard that officers used to knock on his cell door, worried by his late-night studying. Another inmate, serving 14 years for murder, managed a B grade in critical thinking at AS-level.

“When you consider that many of these lads have not been in school since about the age of 12, this is the first chance many have had to receive regular lessons,” says Dr Roy Van Den Brink-Budgen, head of the education team of five employed by City College, Norwich.

Dr Roy, as he is known, was until recently an academic at Cambridge and is chief examiner for critical thinking for the AQA exam board, hence his enthusiasm to see the subject taught.

“The ethos here is: ‘You can do so much more.’ And the lads do find their talents, which have often been hidden beneath the problems they have to deal with.

“This is a pretty special place. People talk of the laddish culture permeating society, but you should have witnessed the day the exam results came out. Those who hadn’t taken any were congregating round their friends to congratulate them on their success.”

There is enough camaraderie for some boys to be able to perform Willy Wonka and The Chocolate Factory, an adaptation of the Roald Dahl story. They happily take the parts of women, donning wigs and speaking in high voices.

“You’ve got to remember that at school most of these lads would have been the biggest pains in the class,” says Hannah Brewer, who works on special projects with the prisoners for a local charity, Aldeburgh Productions. “Here, they are mucking in because they seem to have found a sense of belonging.”

After the show there are presentations of certificates for sporting achievements, and it is announced that all prisoners have signed up to the Duke of Edinburgh award scheme. Two lads are presented with their bronze certificates and will now move on to silver.

Later, one chats briefly to me about his achievement. He seems touched by my interest and squeezes my arm by way of thanks.

It is hard to measure Carlford’s effectiveness in terms of rehabilitation, but three statistics speak volumes: last year there were just 17 disciplinary offences, compared to 1,000 in the main prison nearby; there were no assaults on staff; and only one young man allowed out on home leave two weeks before the end of his sentence failed to return.

“The key to the thing is the attitude of staff,” says Sir David Ramsbotham, the former inspector of prisons who has kept a proprietorial eye on a project he has long promoted.

“They think as a team and have worked hard to relate to the needs of very disturbed youngsters. Another extremely important aspect of the work is that the young people are involved in their own treatment.”