They call it the drinklink, but to the rest of us it's BankLink. It becomes the drinklink when you're still in school but hold down a part-time job in order to finance your social life.

"I was clearing £100 a week working part-time in Dunnes," recalls the 19-year-old girl whom we'll call Fiona although that's not her real name. "I had a ball. I didn't hand up anything at home. I just spent it on clothes and socialising. The more you have the more you spend. I'm only realising now that I could have lived without the money."

According to one Dublin city centre retailer, the teen market is now one of the most lucrative ones around. "It's the 16 to 18-year-olds who have now have the largest disposable incomes," he says. "The shops catering to this market are among the most successful in the city."

Fiona is one of an increasing number of school-going youngsters who spend much of their free time working in part-time jobs and the rest of their free time spending their earnings. Like many students she started working when she was in Transition Year. "I worked in a local shop. I did the 5 p.m. to 8 p.m. shift three nights a week after school and full days on Saturdays and Sundays," she says. "It was all right in fifth year but in final year it was really rough. It was hard to study and work. I found coming in from school and then going to work exhausting. I was fine at weekends, but on Mondays I was really tired."

Opting to continue working during her repeat Leaving Cert year was a big mistake, says Fiona. On the nights she wasn't working, she had little inclination to study. "They felt like nights off and I just wanted to relax."

Second-level schools report a huge increase in the number of students working at part-time jobs. "There have been significant increases in both the number of students working and the amount of time they spend at work during term time," reports a Dublin guidance counsellor. Teachers say that in some schools up to 40 per cent of fifth years now have part-time jobs. "Pre-Christmas in fifth year," she says, "there's a marked increase in the number of students taking part-time jobs and many students continue to work during sixth year to their detriment.

"Many youngsters who take jobs in supermarkets have little choice but to work Thursday and Friday nights and all day Saturday. A lot of students are working 17 hours each week on top of school. This is the equivalent of two days' overtime. Very few adults could sustain that on a regular basis."

Students who work long hours in part-time jobs are noticeably fatigued in class, observes Angela Aherne, guidance counsellor at Ard Scoil La Salle, Raheny, Dublin. "They become run down and are more prone to colds and 'flu than other students. Their attendance can suffer."

These students also lose out on studies. Teachers say that they can point to highly able students who, because of part-time working commitments, fail to achieve their potentials.

"You often see a student who is capable of getting grade Bs at Leaving Cert ending up with Ds," says a Dublin teacher. "Students capable of third-level careers frequently forego the possibility because of part-time work."

Pat O'Connor, principal of St Enda's Community School, Limerick, believes that students can't hold down part-time jobs and study to the level required for the Leaving Cert. "International research shows that to reach your potential you need 26 hours of home study per week. It's difficult to achieve that if you have a part-time job. It's manageable in Transition Year, but the problem is that students find it difficult to give up the money and want to continue their jobs in fifth and sixth years."

A major concern among some educators is the fact that high-earning students are more likely to start drinking at an earlier age. "It predisposes them to enter the drink culture," comments O'Connor. "If they have large amounts of money to spend, they quickly develop a drink habit. Despite the benefits of a part-time job, it can quickly translate into a source of considerable income that is spent on the wrong things.

"Besides, the students develop interests away from their studies. As the job market improves, there will be greater pressures on employers to take in more part-time youngsters. The kid from a poor home is particularly vulnerable and will be driven out of educational achievement."

Guidance counsellors believe that the uptake of part-time jobs is greater in urban areas and that in rural areas there are fewer opportunities for students to work. "We draw on Abbeyleix, Durrow and Ballyragget and you see very few students working in those towns," says David Dwyer, principal of Heywood Community School, Ballinakill, Co Laois.

Only a small proportion of Heywood's students have part-time jobs and the school actively discourages students' working, says Dwyer. "We find that students who get jobs don't turn up in the weeks leading up to Christmas and from mid-May onwards," he says. "We operate on a term-by-term basis and, if a student doesn't sit the end-of-term exams, he or she can't come back the following term."

The school day is particularly long for rural students, he notes. "They are collected by bus at 7.30 a.m. and the last bus doesn't leave until 4.45 p.m. in the evening. Students can't do two jobs. The pressure for points is so great they must give it their total concentration."

However, there are some benefits to part-time work. Angela Aherne points out that summer or Saturday morning work gives students the opportunity to get a realistic view of expectations in the workplace. It also improves their interpersonal and social skills.

In theory they get valuable work experience and explore areas in which they might be interested. Youngsters interested in careers in retailing, for example, may find themselves ineligible unless they have worked as part-timers while at school and college.

Similarly, less academic youngsters who are willing to work hard can gain valuable experience and contacts from part-time jobs which may develop into full-time positions.