Police fired tear gas and water cannon to disperse stone-throwing students outside the landmark National Institute school in the centre of Santiago.
Students clashed with riot police in Chile's capital Santiago during protests that marked the second anniversary of conservative President Sebastian Pinera taking office on Wednesday.
The protests coincided with the 30th anniversary of Chile's return to democracy after Augusto Pinochet's 1973-1990 dictatorship.
During a ceremony in Santiago, Pinera said that 30 years of democratic rule in Chile had been a "fertile" period that dragged eight million Chileans out of poverty.
Shortcomings and inequalities
But he also recognised shortcomings and inequalities that hurt "the soul of our nation."
"We have not sufficiently taken into account the fears and shortcomings of our middle class. We have not progressed strongly enough towards full equality between men and women. We have not fought with sufficient will against the abuses and the privileges of others," said Pinera.
Fueled by outrage at Pinera and the Chilean elite that controls most of the country's wealth, the South American nation has seen since October its worst social unrest since the transition to democracy in 1990.
Thirty people have been killed in the protests, many as a result of a heavy-handed police response condemned as repressive by UN investigators. Thousands have been wounded.
The main aim of the continuing protests is to pressure Pinera to expand social reforms he has already proposed.
'Leave the hard way'
The most serious of Wednesday's disturbances occurred outside the landmark National Institute school in the centre of Santiago, just a few blocks from the presidential palace, where police fired tear gas and water cannon to disperse stone-throwing students.
The demonstration gained momentum through the afternoon, when other protesters joined the students.
"Before, we protested in Plaza Italia, and now we are here," said Rodrigo Lagos, a teacher, referring to the square where most of the protests have begun.
"If (Pinera) doesn't leave the easy way, he's going to have to leave the hard way," added the 46-year-old.
The clashes disrupted traffic through the centre of Santiago for several hours.
Similar incidents took place elsewhere in the capital, as demonstrators responded to social media appeals to protest against Pinera.
Several metro stations were shut because of the violence, and some transport routes to the south of the city were suspended.