Police in Chile have used tear gas and water cannons to disperse thousands of secondary school students in Santiago who are pressing for education reforms.
The protests have been building for a couple of weeks
More than 600 students were arrested in the capital, Santiago, and hundreds of schools were closed across Chile as some 500,000 pupils staged a strike.
Their demands include a new curriculum, free bus fares and no exam fees.
More talks are due on Wednesday to end the dispute, seen as a big test for the new president Michelle Bachelet.
Student leaders and education ministry officials are to resume their meetings in several hours after a first round of talks made some progress but produced no breakthrough.
"I want to ask that we don't make a war of this," declared Education Minister Martin Zilic, saying he was optimistic a resolution could be found.
Protesters said they would continue their demonstrations for another day.
Tuesday's rally in Santiago started peacefully, with thousands of students marching and dancing in the streets of the capital.
But later some of the demonstrators clashed with police, who used water cannons and fired tear gas to scatter them.
More than 700 pupils were arrested, most of them in the capital, and 14 people were injured.
Students and parents criticised what they said were heavy-handed police tactics.
"We are protesting on behalf of our school," Bernardo Ferrada, 15, was quoted by Reuters news agency as saying.
"The bathrooms are disgusting, you can't even take a shower in the locker room, and they don't do anything about it," he said.
Students in Valparaiso, Concepcion and other cities also staged marches to demand changes to the education system.
Protests began several weeks ago when students took over several schools in Santiago, and their strike has now spread nationwide with many pupils staying in school but refusing to attend lessons.
Students are challenging the foundations on which much of the school curriculum is based, the BBC's Americas reporter Will Grant says.
The Constitutional Teaching Law, as it is called, is a throwback to the Pinochet era, and both students and teachers want it comprehensively reformed.
The students also have a number of more practical demands, saying the public education system should get more government funding :
- no fee to sit university entrance exams, now $40 (£21)
- shorter school day instead of proposed eight hours
- free bus fares
Most of those on strike are at state high schools, but the protests also have support from pupils at private schools, including the one attended by President Bachelet's younger daughter.
President Bachelet herself has said she is sympathetic to many of the demands and agrees with the fundamental need to improve the Chilean education system.
The last big protest was in 1972 when a number of student groups challenged the then-President Salvador Allende over his socialist policies.