(Adds details on numbers, violent incidents)
SANTIAGO, May 8 (Reuters) - Thousands of students marched through the Chilean capital on Thursday for the first time since President Michelle Bachelet took power, ratcheting up the pressure on her to fulfill her campaign pledges to overhaul education in the country.
The previous administration of conservative Sebastian Pinera was blighted by dozens of angry and sometimes violent protests by students demanding that changes be made to the privatized education system established under ex-dictator Augusto Pinochet.
Center-left Bachelet, who took power in March, built her electoral campaign around promises to provide better and free education, paid for by a tax reform currently passing through Congress.
But student leaders said on Thursday that there was still not enough clarity on what changes would be made.
"It worries us that of the announcements they have made to date the only thing that they have done is to inject a little more money into this system of segregation, this same system that generates education for the rich and education for the poor," student leader Melissa Sepulveda said to journalists.
Student groups, chanting and waving flags, filled the streets of central Santiago. Police estimated that around 40,000 people took part, while organizers claimed the number was more than twice that.
Although the march was largely peaceful, there were some violent incidents towards the end. Police fired tear gas as some protesters threw missiles and set fire to a car. One police officer was injured.
Some of the student leaders from the 2011 wave of protests were later elected to the lower house of Congress. They include Camila Vallejo, the most high-profile figure, who won a seat in the legislature running on the Communist Party ticket.
Provisionally supporting Bachelet, she and other 2011 movement leaders retain links to the current generation of student activists, and they attended Thursday's march. (Reporting by Fabian Cambero, Writing by Rosalba O'Brien, Editing by W Simon and Peter Galloway)