High above the Salzach’s east bank towers the Hotel Sacher, and atop it for the last few days has been an unusual standard: the flag of Venezuela.

This year’s Salzburg Festival has a heavy load of El Sistema performances, and this was the centrepiece: the National Children’s Symphony Orchestra of Venezuela, all 200 of them, crammed onto the stage of the Felsenreitschule to bash out not just Latin American dances, but to take part in the Festspiele’s central Mahler cycle. It proved once again the sheer emotional power of what El Sistema has achieved and will continue to achieve, given the strength of the cultural diplomacy these young children perform for their nation. Youth orchestras are hardly a new phenomenon, and the long touring schedules of the Simón Bolívar Symphony Orchestra, the Teresa Carreño Youth Orchestra, and now this even more youthful group might suggest a touch of overkill. Swaying double basses, instruments twirled in the air, and endless encores of the “Mambo” from Bernstein’s West Side Story do become a little much after a while. Certainly this concert, with its audience clothed in Sunday-best Lederhosen and clad in the formality of this Festspiele, felt downright weird at times, a mix of genuine enthusiasm and something much more contrived, even disturbing. But the sincerity of these children’s joy in the end left no doubt that those who say classical music cannot change lives for the better, or is somehow beyond the notice of our young people, are wrong.

Musical quality is not really the point of these concerts, although asking Sir Simon Rattle to conduct most of it suggests that as one aim. After all, how convincing can Mahler's First Symphony with octuple winds, seventeen double basses, fourteen horns, and five tubas really be, let alone one played by pre-teens? So this cannot be a full, regular review. That said, it was clear to anyone who knows Rattle’s Mahler that this was an interpretation cut from the same cloth as his work with the Berliner Philharmoniker: tightly detailed, maddeningly and fussily so, to the detriment of the necessary longer line. (If anything, the rawer quality of the Children’s Orchestra added a welcome imprecision, impetuosity, and unpredictability.)

But the focus should be on the players, and there were stars aplenty. Take, for instance, the orchestra’s floppy-haired principal cellist, standing inches shorter than his cut-down cello and yet attacking Mahler’s counterpoint with a rare zest and exactitude. Or the two principal clarinettists, the younger particularly fine in a long, sultry solo in George Gershwin’s Cuban Overture. Or the bombastic accuracy of the brass, the tenderness of the leader’s work on the violin, and the fragile morbidity of the double bass soloist in the Mahler’s third movement invocation of “Frère Jacques”. And more importantly, the entire orchestra played together with a real zest, an irresistible rhythmic energy, and especially in the Mahler, a special sense of concentration. They tore into the inferno of that symphony’s final movement, and even the stoutest of hearts could not fail to be moved by the triumph twenty minutes later.

Rattle was not the only conductor on the podium, for Jesús Parra took over for the El Sistema showpiece, Alberto Ginastera’s suite from Estancia. Parra, conducting a day shy of his nineteenth birthday, has a style familiar to anyone accustomed to Gustavo Dudamel: all bite, all downbeat, and an embodiment of the musical flow rather than a technician. He drew a cleaner sound than Rattle from the orchestra, and shaped Estancia’s dances with a rollicking power.

The message of this concert, though, was more important than the medium. Dozens of teachers came on stage after the Mahler, heralded with screaming praise from the orchestra. Yellow, blue, and red garlands were hung around Rattle’s neck by the string principals, that first cellist was picked up for a hug, and the double bass soloist attempted to divert applause back to the conductor during his lone bow. The ovation went on forever, punctuated only by the “Mambo” (with audience participation, cheesily rehearsed by Rattle in German) and Parra’s return for some “ethnic Latin American music”: the Radetzky March, as it turned out, the young conductor marshalling the audience’s applause as if he were Herbert von Karajan.

Don’t let anyone tell you music isn’t relevant. It is.