`It could be anyone," choirmaster John Dexter tells the choirboys of St Patrick's Cathedral, as they rehearse carols in one of the music rooms in their school across the road from this famous Dublin building. Dexter is referring to the tradition of choosing a soloist to sing the opening verse of Once in Royal David's City at the Christmas services in St Patrick's.

Generations of Irish people have stuffed turkeys and wrapped presents on Christmas Eve, while listening to the choirboys of St Patrick's singing in the hugely popular service of Nine Lessons and Carols. Broadcast live on RTE Radio One, it's the longest-running programme to air on the station.

The signature carol is Once in Royal David's City, with its soloist's opening. People throughout Ireland pause in their Christmas frenzies to listen to the first verse of this carol, the delivery of which commands a few timeless moments of attention.

Charlie Bowder (13) sang the opening verse of the carol two years ago. "You get told it'll be you at the final practice, so you do know a bit beforehand," he explains, slightly regretful of the notice. "At King's College, Cambridge, they only tell you as you're walking in procession into the church on the night. I'd like that," he says with glee. "There'd be more tension!"

Charlie's face still lights up when he recalls his solo. "Your name isn't on the programme or anything like that. You're just a voice in the choir to the people in the cathedral. But you feel pleased for a long time afterwards. It'll be something that'll always stay with me."

Darragh Ware (12) is the current head soloist and a school medal holder for his choir work, and therefore a potential choice for this year's Christmas honour. The boys agree that there is much speculation among them at this time of year as to who might be picked.

"You are always wondering who it will be," Darragh confirms. "We're always talking about it."

To watch Dexter at work in the early morning choir practice is like watching a diviner holding the hazel and waiting for it to twitch as it senses water. To an untrained ear, it's impossible to distinguish between the quality of the voices - all of which sound uniformly pure - but Dexter can identify the individuals who reach the truest notes.

After listening to them singing in unison, he calls out various names, and those boys then sing a line or two of the carols, as he tries out their solo ability. This is when you do hear differences in the voices, and also, how strongly revealed are the character and personality of those behind the voices. One boy is sent off in cheerful unembarrassment to remove chewing gum from his mouth - noticed by Dexter while singing solo. He returns sans gum to lift high notes as effortlessly as Samson tossing a few trees around.

The choirboys' days at school are long, with early singing practices, usually followed by matins, and often ending with evensong. They're different from other children of similar age in that their timetable means they lose out on free time. They have to be in school for 8.30 a.m. every day, and often do not leave until after 6 p.m., when evensong is over.

"Life is full of sadnesses," Darragh says philosophically. "No, I meant it's full of disappointments." He stops, and frowns, a bit confused about what he does mean, but it's clear that he understands his particular schooling demands some personal sacrifices, which for now he is happy to give.

Both Charlie and Darragh talk fluently about the technical structure and theory of music. What about the complex lyrics of the psalms and hymns? Do they understand what they mean?

"The words are picked to fit the music," they explain, stressing the importance of the music above the words. "Although we did find out what `terrestrial ball' was," Darragh adds. "We didn't know what it was. It means the world."

Across town, the boys at the Gate Theatre who are currently acting in the evening productions of Oliver Twist are rehearsing for a very different kind of Christmas performance. No anonymous achievements for them: their names and pictures are carried prominently in the theatre programme.

The seven young actors range in age from 12 to 16. Oliver is played by Oliver Darmody (13). They bound out of the Green Room, where they wait between appearances, and come tearing down the stairs into the bar area like a happy human train.

"Hello! Hello! Hello!" they shout, flopping down on the floor and whipping out their mobile phones, automatically putting them down where they can see them. Well, you never do know when that phone will ring with the next offer of work. .

Unlike the choirsters, most of these boys are at ordinary school, attending drama school or workshops out of school time. So how are they managing school on top of their four weeks of rehearsals, and a performance time which stretches until February?

"Well, the schools have been on strike a lot," they point out. "And the theatre works around the schools." Then they roar with laughter. "Seven lads in the Green Room! It's like being in a classroom unsupervised!" At this point, their chaperone, Adele Synott, whom they clearly adore, points out that she is there to supervise. "We do lessons. And play cards."

Beyond Oliver, Charley is played by George McMahon (16), and the Artful Dodger by Ciaran O'Brien (15). The other parts are referred to in the programme as boys one through to four. "We do get our own lines." says Barry McGuinness (12), Third Boy. "We're not rejects!"

Several of the boys have worked together before, and most of them have previous experience, either on stage or television. They all say they want to make a career in acting. "It can't happen to everyone, but it will happen to most of us, because we're very good," is Barry McGuinness's theory.

Now that the show has opened, they have to be in the theatre no later than 7.20 p.m. each evening, and they remain until the end, to take their bows. "We mess a lot, but we don't mess on stage; that's serious," says Conor McGlade, Second Boy. For George McMahon, the best thing about being in the show is the opportunity to "go back in time and see what it was like then".

Argument ensues. "It's not a true story," yell the others. George is unperturbed. "Well, there were workhouses," he says.

It's time for them to go back on stage. Does anyone else have anything to say?

"Oh yes," answers Oliver Darmody, thrusting out his cupped hands. "Please sir, can I have some more?"

Service of Nine Lessons and Carols will be held in St Patrick's Cathedral this Sunday at 3.15 p.m. and on Christmas Eve ticket only) at 4 p.m.

Oliver Twist runs at the Gate Theatre until January 27th.