Tens of thousands of students in Chile have resumed their protests for free education with marches in major cities.
The march in the capital, Santiago, was largely peaceful, but there were isolated clashes, authorities say.
Riot police said that they had been attacked with petrol bombs. Police used water cannons and tear gas to break up one group of protesters.
Chilean students have been staging protests for free, high-quality education since 2011.
Wednesday's action was the second nationwide protest this year.
The police estimated the number of protesters in Santiago at more than 37,000 but organisers say 80,000 people took to the streets.
There also were protests in other Chilean cities, including Valparaiso, Concepcion, Temuco and Valdivia.
On the first national marches of 2013, in early April, more than 100,000 participated.
Although Chile's education system is regarded by many as one of the best in Latin America, students argue it is deeply unfair.
They say middle-class students have access to some of the best schooling in the region, while the poor have to be content with under-funded state schools.
There are no free universities.
The campaign for educational reform is the biggest protest movement Chile has seen since the return to democracy in 1990.
It started with a wave of mass demonstrations in 2011, which carried on throughout 2012.