Everything else is in place for the holiday season: the parties, the Menorah candles, demonic shopping crowds, British tourists on the subway, Macy's and its Santa Land – a long queue of children and their parents marshalled by strangely mature elves who slouch and roll their eyes - but not the weather.

So it was warm last Thursday for one of the more recherché events in New York's holiday calendar: the end of term musical at the Fiorello H. LaGuardia High School of Music & Art and Performing Arts – otherwise known as Music & Art, otherwise known as "that school from Fame ". The annual musical is the only show in which all five divisions of the school - music, art, drama, dance and technical theatre - collaborate. And this year the school, which was opened in 1936 to nurture gifted students and has inspired a musical and TV series, is doing West Side Story.

The show is always an event – sold out, attended by agents and talent spotters, and reviewed in the New York Times. And this year it is slightly more so, with the school celebrating the 20th anniversary of its incorporation of the School of Performing Arts. West Side Story is relevant too: the school is on Amsterdam Avenue at 64th street, a short walk from the old warehouses and battered waterfront where the musical was set, but which are fast disappearing under controversial developments.

Not quite glamorous enough for a ticket to one of the evening performances, I came to a morning refresher rehearsal, attended by me, the production staff, a few interested alumni and about 800 middle school children, aged 10 to 13, from local schools.

As the kids came tumbling into the 1,200-seat school theatre, all slightly delirious with school-trip excitement, Harry Shifman, the director of the show, was setting up video equipment. In the programme notes, Shifman, a director and playwright who has worked with the school for many years, thanks "the little geniuses" of LaGuardia, and as he waited for the performance to start, he paid them tribute once again.

"At this stage, they all want to be on Broadway, to be a star, they want everything," he said. "They have such life, such energy and they grow so much in the rehearsal process, it is something to behold."

Shifman added that some of the cast are ready to work – a glance through the programme showed that many have appeared on TV and stage already – while the rest are still blossoming. And watching the show, it was difficult to remember exactly what I was looking at, polished students or celebrities-to-be.

Most of the time, there was the smoothness and the swagger of a professional production. The singing, especially, was effortless and Maria (15-year-old Karen Rodriguez) swanned through her numbers without seeming to think. And the face-offs between the Sharks and the Jets were all the more believable because everyone was so young.

That great song, Gee Officer Krupke ("We're down on our knees, 'Cause no one wants a fellow with a social disease") was the best of the lot – with the Jets using their bodies to suggest the courtrooms and therapy offices that even a middle school audience knows plenty about.

As for the immigrant tensions of the play, that felt like old news. I want to live in America is not a song you hear a lot in New York these days. And the diversity of the cast (quite rightly mixed between the gangs) made the Manhattan waterfront look more like a Gap advert than an ethnic battleground.

Only occasionally there were glimpses of teenage tentativeness, of recently grown legs and arms and voices, and flashes of hesitancy in the difficult, climactic scenes, like Tony's meeting with Maria after he has killed her brother. At these moments the crowd of pre-teens was ruthless: they whispered, guffawed and flipped out their mobile phones, splashing little dots of light around, before setting down when the action came around again.

But ultimately the absurdity of musical theatre won out, with the LaGuardia students engrossing their future fans. The death of Tony, an event seen – I'm guessing – for the first time by most of the audience, was greeted with rank hysteria. "Nooooooo! Nooooooooo!" screamed the kids behind me, ignoring the continuing action.

And they were only slightly less excited by the love story. Although there mutterings of "whatever" in response to the schlockier moments, kissing was definitely cool.

As Tony and Maria's lips met for the first time, one boy yelled out: "Yeah! I gotta come to this school!"

Slices of New York