The prize, awarded by a jury headed by Sean Penn, the Hollywood actor, came at the end of the world's most prestigious film festival.

Directed by Laurent Cantet, the docudrama used real students and teachers and was shot in a raw, improvisational style. It was the first French film to win the top prize at Cannes since Under Satan's Sun in 1987.

There was also British glory, with the prize for a film by a first-time director going to London-born filmmaker Steve McQueen, whose Hunger chronicled the last six weeks of the life of the IRA hunger striker, Bobby Sands.

Matteo Garrone's Gomorrah, a study of the criminal underworld in Naples, took the grand prize, while Paolo Sorrentino's Il Divo, a lively portrait of former Premier Giulio Andreotti, won the jury award.

Benicio Del Toro won the best-actor prize for Che, Steven Soderbergh's four-hour-plus epic about the Latin American revolutionary Che Guevara.

Presented as two films, it follows Guevara and Fidel Castro's guerrilla campaign to overthrow Cuba's government in the late 1950s and Guevara's downfall and execution after trying to foment a similar rebellion in Bolivia in the 1960s.

The Cannes jury awarded special prizes to Clint Eastwood, who directed the competition film Changeling, his warmly received missing-child drama starring Angelina Jolie.

After the awards ceremony, the festival closed with the premiere of Barry Levinson's What Just Happened? – the story of a fading Hollywood producer trying to lift his career, starring Robert De Niro, Bruce Willis and Sean Penn.