Critics suggest that it is simply a doss year, an extended holiday which is usually paid for by the Bank of Mum and Dad.
Its advocates, on the other hand, argue that it makes students more mature, giving them a sense of independence and a chance to see something of the real world before they go on to third-level education.
Although the gap year is not nearly as popular here as in Britain, where up to a fifth of college-goers take one, there are signs that it is now becoming a fashionable option for Irish school leavers.
A growing number of Irish teenagers, particularly in affluent areas, are following the example of Prince William, who was famously pictured cleaning toilets in a remote part of Chile on his gap year. As a volunteer for the charity Raleigh International, William helped build new walkways in the mountainous area and taught English in a local village.
Some gap-year students, or "gappies'' as they have become known, are much less diligent, spending much of their time lolling about on beaches in places such as Thailand. Others spend their time working and saving for college.
Career guidance counsellor Andree Harpur says the gap year is growing in popularity in Ireland because parents see that many of the voluntary schemes available are now well-organised.
"It's not just a matter of a teenager heading off on a train to Marrakech any more. Parents feel reassured when they see a programme that has been put together carefully," she says.
"I know of students who have got enormous benefits from a gap year. They might not have decided what they wanted to do. Say, for example, if they were considering social work, some kind of voluntary work could help them to make a decision.''
As a careers advisor, Andree Harpur believes gap years are often looked upon positively by employers.
"If you are prepared to get on a plane to go to work somewhere on the other side of the world, you are showing that you are adaptable. You are open to new ways of doing things.
"But it has to be planned properly and it should be clear that it will only last a year. There is a danger that a student with wanderlust will not continue with their education at all.''
Gap-year students who want to do voluntary work should check carefully the credentials of the organisers of the scheme. Is the work genuinely helpful, or is it just a profit-making venture?
The huge growth in the gap- year market has given rise to some spurious schemes that can do more harm than good, according to Voluntary Service Overseas, an international-development charity.
VSO recently warned that badly planned, so-called "voluntourism" schemes could have a negative impact on young people and the communities they worked with.
In one case, reported by the Guardian, a group of villagers in South America returned home from work to find that their houses had been painted by volunteers without their permission.
Another gap-year student was asked to survey an endangered coral reef in Madagascar, only to find that the work was pointless because the reef had been surveyed 200 times by other volunteers. Such surveys probably just damaged the reef.
There are a number of more reputable gap-year voluntary schemes that are non-profitmaking.
Lattitude, formerly known as Gap Activity Projects, is a well-established British charity which has taken a number of Irish volunteers abroad.
"We ensure that we only offer voluntary work that is going to be worthwhile," says Lattitude spokesman Ben Clifton. "It has to be suitable work that improves the quality of life of the people concerned.''
The European Voluntary Service (EVS), funded by the European Commission, offers young people the opportunity to do voluntary work in other European countries.
Unlike many other gap-year schemes, the scheme does not require volunteers to pay a fee.
Gap-year students can also stay in Ireland and do voluntary work here. Others take on paid jobs in order to get work experience and to make themselves financially secure before going into college.
'MY YEAR OUT HELPED ME'
Barry Colfer, a student of business and law at UCD, said his gap year after leaving school was a great help when he was deciding what he wanted to do.
"I had a look at doing volunteering work abroad, but I found that it was too expensive. Instead, I decided to get a job in Waterford. I had jobs in a restaurant and a supermarket.
"It was useful taking a gap year, because I was not really sure what I wanted to do when I left school. I had applied for physiotherapy and I was accepted. During my gap year, I decided that it was not really what I wanted to do. Instead I applied to study Business Law, and I don't regret the decision."
Barry, who is currently President of the UCD Students Union, says: "Taking a gap year helped me to appreciate the value of money and the importance of education.
"I don't take free education for granted and I realise the importance of upskilling. I have great respect for the jobs which I did, but I realised that I did not want to stack shelves all my life."
PROS AND CONS OF A GAP YEAR
A break from studying. More study may be too much after the Leaving Cert.
More time to decide what to do at third level.
Can enhance CV.
Experience of new cultures, skills and languages.
Greater self-confidence and maturity.
Volunteers may find work rewarding.
Can put finances under strain.
Work may be boring, mundane and/or repetitive.
Finding a good placement may be difficult without special skills.
Students may drop out of education all together.
Student might not be able to cope with emotional strain of voluntary work
Source: National Centre for Guidance in Education