During his 12 years in the Army, Chris Thompson did two tours of duty in Northern Ireland in the early 1980s. “It was a massive eye-opener,” says Mr Thompson, a former sergeant in the Worcestershire and Sherwood Foresters.

“If there wasn’t a riot, there’d be a bomb, and if there wasn’t a bomb, there was a shooting. There seemed to be something every hour. I was only 19, but I had to grow up fast.”

It didn’t quite prepare him, however, for his next challenge: teaching. “It was a bit of a shock to the system,” admits Mr Thompson, who qualified as a teacher three years ago. He now teaches PE at Thomas Deacon Academy in Peterborough and is contingent commander of the school’s burgeoning Combined Cadet Force (CCF).

“In the Army, you give an order and they do it, but a stroppy teenager may tell you to get stuffed. Instead of being a dictator, I had to become a diplomat. I had to keep selling the idea of sport until they became addicted.”

Now they keep coming back for more. He was told he would be lucky to get 50 pupils signed up for CCF when it started in September 2007, but now he has 120. Were it not for budgetary restraints, he believes he could double that number tomorrow.

Mr Thompson may not have 100 men and women doing press-ups on his command anymore, but once he has sold the concept to them, 40 previously uninterested pupils will get down on the ground and give him 20. And if they do not do it properly, they do it again.

“I love the old-school discipline, and the pupils respond to it really well,” he says. “In CCF I teach them to stand up straight, look people in the eye, take their hands out of their pockets and give respect when due. They use what they’ve learnt in the rest of the school. It’s saved some from exclusion.”

If the Ministry of Defence (MoD) gets its way, a much greater number of ex-forces personnel will follow in Mr Thompson’s footsteps. A tailored teacher training course, specifically for those who have served in the Army, Navy and RAF, is now being devised, with the first recruits due to start this autumn. The two-year Open University course, which includes working in two schools, will eventually lead to a BSc in secondary education in physics.

It is hoped that serving members of the military, who work in technical jobs such as weapons maintenance or engineering, will help stem the shortage of science and technology teachers. If it is a success, the route may be extended to other specialists and other subjects.

But soldiers will not just be plugging a gap. The hugely successful Troops to Teachers (T3) programme in the US suggests that former service personnel bring a whole gamut of skills and attributes to the classroom, including self-confidence and discipline.

The T3 scheme retrains soldiers with a minimum of 10 years’ experience - and a degree - as fully certified teachers. Those with lower qualifications are retrained as vocational teachers. About 16,000 ex- servicemen and women have qualified since the programme launched in 1994.

More than 90 per cent of headteachers involved in the US scheme say former service personnel are more effective than other teachers when it comes to managing behaviour and improving grades. And they do not leave at the first sign of trouble. Some 88 per cent of T3 teachers remain in the profession three years after they qualified, according to a report by the think-tank Centre for Policy Studies. The overall three-year retention rate for teachers in the US is 50 per cent.

Before the election, the Conservatives expressed support for the idea, saying ex-forces personnel could bring much-needed discipline to the classroom. Although the prospects for a UK version are still unclear following the formation of the Coalition, the Tories argued that a British version would also act as a good source of positive role models.

Roy Robertson, a former primary school teacher based in Falkirk, backs the concept all the way. He was a part-time soldier with the Ulster Defence Regiment in his native Northern Ireland at the height of the Troubles in the early 1970s, before moving to Scotland and joining the Territorial Army.

“Pupils need boundaries and soldiers are very good at imposing that,” he says. “They know about self-discipline and can pass it on to pupils.”

Yet not everyone agrees that all ex-servicemen and women would make such good teachers. Behaviour seen as a virtue in the forces - such as shouting orders and unerring obedience - sit uneasily with classroom values based on mutual respect.

“Troops are obliged to obey orders without question,” says one teacher, who asked to remain anonymous. “I suspect anyone who is used to barking out orders is going to struggle the first time a class doesn’t stand to attention.”

And there is an even more fundamental question as to whether it is appropriate for ex-forces personnel to enter teaching. Of the 25,000 people who leave the armed forces in Britain each year, only about 60 become teachers, according to the MoD. In stark contrast, about 2,430 veterans are currently in prison, admitted Maria Eagle, the former justice minister, earlier this year.

A larger proportion enter the unskilled jobs market. Although they may show great potential, few have the qualifications needed to enter the classroom.

While 7,000 of the annual UK service leavers are officers, many with some experience of higher education, the majority of ex-servicemen joined the forces on leaving school and will have no degree.

MoD resettlement packs include advice on teaching careers, but many will be put off by the prospect of postgraduate training.

It took more than that to deter James McGough. At the tender age of 17 he joined the Army, which is where he stayed for the next five and a half years.

“I thought I would love to be a teacher, but I truly believed it was above me,” says Mr McGough, who signed up to the Army primarily to escape his home city of Sunderland. “You would never expect someone from my background to go to university.”

After a stint on a building site in London, he returned to the North East and began the long slog of improving his qualifications. After a number of taster courses, he became hooked on biology. He took two A-levels, brushed up his English and maths and took a three-year pharmacology degree. Even then, he was unsure if he was up to teaching, but his course leader persuaded him it was within his reach. A science PGCE in Hull followed, which is where he got his first teaching post.

“It was incredibly hard work getting there, but the teaching itself was an absolute doddle,” says Mr McGough. “I did what I needed to do to get a standard pass in the theory part of my training, but I was getting grade ones in my placement schools. I felt I had come home to roost.”

After his first teaching year, Mr McGough was made deputy head of science. By the end of his second year, he was promoted to head of department. He is now science leader at the Community Science College @ Thornhill in Dewsbury, West Yorkshire.

More senior military figures can have an easier ride into education. Steven Handford, a regional director for the charity Skill Force, already had a degree when he went into the Royal Regiment of Fusiliers in 1989 as an officer. So when he left as a captain six years later, having done tours in Norway, Northern Ireland and Jamaica, he was well set to start an English PGCE at Cambridge University.

“I lost my `green’ military head quite quickly in the classroom,” says Mr Handford. “It would have been easy to become a sort of Captain Peacock character (from the sitcom Are You Being Served?). If you’re not careful, you could become a figure of ridicule.”

Instead of dining out on his military background, Mr Handford quickly adapted to his new environment - a secondary school in Sunderland.

“You can’t shout at kids, you can’t send them to jail and you can’t shoot them, so you have to find an alternative way,” he says. “Luckily, I think the military taught me to have some flexibility of mind, and I was able to look at myself and see what new skills were needed.”

Some of those skills he already possessed: organisation, rigour, tidiness and discipline were ingrained, as was the ability to design a scheme of work with a plan B attached. Eventually, however, Mr Handford became disillusioned, feeling he was imposing unrealistic standards on his pupils. “I was flogging Tennyson’s The Lady of Shallot to kids who struggled to read and write,” he says. “It didn’t fit with their lives.”

So he joined Skill Force, which sends ex-service people into schools for one day a week to work with largely disaffected Year 10 and 11 pupils. Like many others from an Army background, Mr McGough says there is no doubt that his military training has taught him about the importance of discipline and routine. But he is careful not to play on a cliched macho image, or his imposing physical presence.

“The best disciplinarians I know are small, slight women,” says Mr McGough, who is 6‘2”. “I don’t consciously use my background, but I guess it does have an impact on how I teach. I’m probably one of the stricter members of staff.”

That means pupils know where they stand with him - quite literally in some respects. They quietly line up outside his classroom before lessons, before getting their books, equipment and lesson planners out without a fuss when they come in. They also know that late coursework will not be tolerated.

In return, Mr McGough marks and returns their work quickly, and adheres to the school’s positive reinforcement policy.

Mr Thompson has a similar attitude. Now that pupils have stopped asking him how many people he has shot or killed, he has started to reveal a bit about himself. He tells them that he has had a similar upbringing to some of them, and that there is light at the end of the tunnel.

“They know I’ve lived a bit,” Mr Thompson says. “An Army motto is that you’ve got to `improvise, adapt and overcome’, so whatever is holding the pupils back, I emphasise that they’ve got to get it sorted one way or another.”

While some will doubt the wisdom of employing ex-forces personnel in schools, Mr Thompson’s experience is that many hard-to-reach pupils do respond well to Army-style discipline and dedication. And if the MoD’s scheme in schools takes off, the presence of former members of the armed forces could become the norm rather than the exception.