The Simon Bolivar Youth Orchestra of Venezuela, which caused a sensation at last year's Proms, is the product of an extraordinary music education system that has been running for more than 30 years. Children as young as two get intensive music lessons designed to steer them away from the dangers of the street. With Scotland now trying its own version of the scheme, Alan Yentob investigates the phenomenon and meets its most successful graduate, 27-year-old conductor Gustavo Dudamel, who next year becomes music director of the LA Philharmonic.