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The deafening, tub-thumping beats and shouts of defiance from trade union marchers were joined by new voices for the latest protests in Paris - students as young as 15.

Their protests started early. By 0930 a group of 300 students had mounted barricades across the road at Place de la Republique, and had begun to chant and throw bottles at police.

The teenagers seemed to be playing at rebellion - shouting and taunting the police and then running, flushed with excitement, to tell their friends.

This was the sixth of the co-ordinated national demonstrations against plans to reform the pension system, and the real difference this time was the protesters' ages.

Some seasoned trade unionists said the protesting students would certainly attract the attention of the government.

Student groups were pivotal in forcing the government to back down in both 1968 and 2006 after they joined trade union protests.

All along the packed boulevards large groups of secondary school students shouted their objections to the proposal to raise the age of retirement from 60 to 62.

"It's impossible to think of working that long," said 15-year-old Julie Allard.

Her gaggle of girlfriends chipped in excitedly: this was their first protest, they said, but they "really felt strongly" about the issue.

Another student, Florent Soubier, had a more reasoned argument: "It's hard enough to get jobs already, so they will make people work longer and do nothing about youth unemployment."

By midday, the march had started from Place d'Italie.

French flags swirled past a huge puppet of Marianne, the female embodiment of France embossed on the republic's stamps and money.

A theatre group took turns to attack her with vultures on the end of sticks: a metaphor, they said, for the dismantling of the welfare state, and France itself.

The unions were joined by the Socialist Party, and various other leftist and anti-capitalist groups. In their midst, causing a pile-up of floats, security, marchers and banners, was a flushed-looking Segolene Royal, the Socialist presidential hopeful for 2012.

The Socialists are trying to use this moment of anger against the government to their advantage.

The mood remained buoyant along the route of the protest.

But after the violent protests on Monday, the authorities were taking no chances.

In each side street large groups of riot police stood ready for action.