Violent clashes have broken out again in Chile's capital as small groups of hooded youth clashed with police and marred an otherwise peaceful march by as many as 100,000 students demanding changes in public education.
Two huge marches, organised with approval from authorities, converged in a demonstration in Santiago calling on President Sebastian Pinera to expand the central government's role in educating Chileans.
The changes sought by students, who have been protesting and boycotting classes for nearly six months, would fundamentally overhaul a school system that has been steadily privatised since the 1973-90 dictatorship.
Pinera has insisted on more targeted reforms, such as increasing state subsidies so that poor students can afford to attend private institutions.
As Wednesday's demonstration broke up, small groups confronted police and violence spread quickly. A gas station was attacked, with vandals spraying flammable gasoline around.
Police hosed the area down and kept others away, cutting off electricity to avoid sparking a huge fire.
Smaller protest marches on Tuesday also had a violent fringe element of hooded rioters who tried to attack a gas station and set fire to a bus whose passengers had fled.
Student leader Camilo Ballesteros has said such violence only strengthens the government's efforts to paint striking students as out of control.
On social networks, student activists are increasingly questioning who is responsible for the violence, with some raising the possibility that pro-government instigators are fostering trouble.
Chile's deputy interior minister, Rodrigo Ubilla, said on Wednesday that two police officers were injured overnight and 263 people were arrested nationwide "in another day of violence and destruction.''
No additional numbers of arrests and injuries were immediately available after Wednesday's demonstration.
Pinera has rejected the students' core demand that Chile provide free public education to all its citizens, arguing that this would force poor taxpayers to defray the costs of the rich.
Students say the costs of free quality education could be more than covered by making the rich pay more in taxes.
Pinera has sent his own proposals to the Congress and appointed a commission of experts to provide him with further ideas in January.
Chile's political leaders on the right and left both say that the education debate will have to be resolved in Congress.