Friday afternoon in Montalban, a concrete suburb of Caracas. I'm climbing the stairs of a cheerless modern block when, suddenly, a blast of Beethoven's Ode to Joy almost knocks me back down again. The sound is big and bold, if not exactly in tune; it is full of the exuberance with which Beethoven, by then deaf, set Schiller's words to music. The poet later said his work was "detached from reality". As I crest the stairs, so too is the sight before me: an orchestra of 70 Venezuelan children in shorts sawing and scraping out those unmistakable uplifting chords.
This is a nucleo, one of 270 purpose-built music schools across Venezuela, where children as young as three play in orchestras for three hours every afternoon. Next door, a smaller group of older children plucks "Moliendo Café", a traditional national tune, on mini-guitars, while, downstairs, yet another orchestra is playing Handel. This is all part of the now world-famous El Sistema, Venezuela's social improvement programme, started 37 years ago by the visionary economist and musician, Jose Antonio Abreu. Meaning "The system", it's a drab name for a programme that has changed the lives of hundreds of thousands of impoverished children, and produced the famous Simon Bolivar Youth Orchestra and its legendary conductor, Gustavo Dudamel.
El Sistema was founded in 1975, but it was only in 2007, when Dudamel and his orchestra played a celebrated Prom at the Royal Albert Hall, that anyone in Britain took note.
As part of the London 2012 Festival, Dudamel and his orchestra are returning for a four-day residency at the Southbank, starting this Saturday. The two centre-piece concerts sold out within weeks when tickets went on sale last year, but there's still plenty to see, with more than 60 events planned, as the Festival Hall is turned into a giant nucleo. As anyone who has seen them will tell you, students of El Sistema play with a unique vitality, swaying in their seats or even bopping up and down. Above all, they grab the scores of dead European composers and turn them into life-affirming musical firework displays.
It's easy to get carried away, but that's partly the point. As one teacher tells me, El Sistema is chiefly a social project, that happens to use music as its tool. The aim is to guide underprivileged children away from a life of crime and drug-taking, which, in Venezuela, is all too easy to choose. Despite President Hugo Chavez's ambitious programmes for free health care and education, his country is overrun with violent criminal gangs, especially in the capital. The Venezuela Violence Observatory, an NGO, named 2011 as "the most violent [year] in Venezuela's history", with 19,336 murders recorded, up 30 per cent on 2010. Many more go unreported, and Venezuela is thought to have one of the top-five murder rates per head in the world. Kidnappings are also on the up, while US analysts say more cocaine is passing through the country.
No wonder they insist on driving me round town in a blacked-out jeep. But once security guards have waved us through the gates of this purpose-built compound, all anyone is thinking about is music. The school day finishes early in Venezuela, at 2:30pm, giving nucleos all afternoon for rehearsals. You might have thought a child would be tired after a day's work (school starts at 7am). You might even wonder why they'd rather tackle a symphony than kick a football. So in a pause between movements of Vivaldi's Concerto Grosso, I ask Natalie Velazquez, a 13-year-old first violinist, why she's here.
"I've been coming here since I was three," she says. "I'm here because I like it." Her favourite composer is Tchaikovsky, and she finds Mahler the most challenging. She listens to classical music at home with her parents – her father's in the military and her mother's a teacher – though she also likes all the usual teenage favourites, such as Lady Gaga. What do her non-nucleo friends make of El Sistema, I wonder. She's not bothered: "They have a lot more free time," she laughs.
And it's not all about the music: Natalie has made many of her best friends in the nucleo. She has an older brother and a younger sister who also play there, and her parents, she says, are extremely proud of the progress she has made. She plans to study engineering at university, though she doesn't rule out playing violin professionally.
Which is not so far-fetched. That morning, I was shown round the spanking new Centre of Social Action through Music – El Sistema's headquarters, which boasts three major concert halls and dozens of rehearsal rooms. Any of the 310,000 students currently in El Sistema can use the space here to practise whenever they want. Concerts are frequently put on to packed houses, the audiences brimming with proud parents. Abreu started his project in a garage; now banks give him millions. Two new buildings by Frank Gehry are planned.
And the good news is spreading. Some critics ask why so much attention is paid to Venezuela's youth orchestras when, back home, fewer state-school children have access to musical tuition. In 2010, an ICM Research poll found only a third of children in the UK played an instrument, compared with two-thirds in their parents' generation, while a 2005 study suggested that as few as 8 per cent of state-school children aged from five to 16 years played an instrument. But when the stars of El Sistema unpack their bows at the Southbank this week, they will be with resin-lobbing distance of a very similar success story unfolding nearby.
It's called In Harmony Lambeth, and is part of a wider programme being unrolled across England, with projects in Liverpool and Norwich, supported by the Arts Council. Scotland already has its own scheme, Make a Big Noise, which has taken the Sistema name. The cellist Julian Lloyd Webber set up the English version after a trip to Venezuela. I look in on a rehearsal at Wheatsheaf Hall, in Vauxhall, a volunteer-run community centre founded by a Victorian philanthropist. Caracas feels a long way away, but the buzz is the same. Everyone in this room wants to be here; it's not at all like my memories of school orchestra.
"It's fun," says Daniela Miranda, nine, one of the first violins. "You're learning something, and they say also that if you learn how to play violin, you also learn how to do maths. I'm now in the higher level." Kedus Joseph, also nine, is section leader of the violas, and a big fan of Holst. He plays at home so much that his three brothers are quite jealous. "They're always asking me to play 'Twinkle Twinkle Little Star'."
In Harmony Lambeth will perform at the Simon Bolivar Orchestra's Southbank residency this weekend. And Arts Council England has announced funding for four more In Harmony projects across the country. In Venezuela, the children I spoke to thought nothing of aspiring to be professional musicians, and, in Britain this week, we will get the chance to hear some of those who did. But what of our own budding talents? Will Daniela and Kedus keep playing when they grow up? The answer is a definitive "yes". As I leave Wheatsheaf Hall, the orchestra strikes up a jaunty rendition of "La Cucaracha", and, suddenly, Venezuela doesn't seem so far away. Perhaps I have just seen a new generation of professional musicians in the making. Perhaps they will one day form an orchestra as famous and well-travelled as the Simon Bolivar. And perhaps, one day, they will even play a residency in Caracas.