Police Move in on Mexico City Protesters Thousands of striking teachers briefly seized control of the historic heart of Mexico City on Friday, blockading the Zocalo plaza armed with metal pipes and wooden clubs. Minutes after a late-afternoon government deadline, riot police started pushing into the area, firing tear gas and ducking hurled rocks in a confrontation culminating weeks of protests against an education reform. The teachers used steel grates and plastic traffic dividers to block the streets leading into the Zocalo, home to the Metropolitan Cathedral, Templo Mayor and National Palace, some of the city's best-known tourist attractions. Hundreds of Mexico City and federal riot police massed on the other sides of the barriers, then swarmed into the square past the famed Aztec temple, chasing down and arresting protesters. Mexico's government had promised that Independence Day celebrations, including the traditional presidential shout of independence from a balcony overlooking the square, would take place in Zocalo Sunday and Monday. The president's office pointedly released an official schedule in the middle of the protests, noting that the independence "shout" would take place at the National Palace at its usual time Sunday night. Manuel Mondragon, the head of the federal police, warned on national television that police would move in at 4 p.m. local time. The teachers, many veterans of battles with police in the poor southern states where they live, promised not to move from the square where they have camped out for weeks, launching a string of disruptive marches around the city. Shortly after the deadline, the police swarmed in, shooting tear gas from specially equipped fire extinguishers and tossed flash grenades. Protesters hurled sticks and chunks of pavement broken from the street. Within a half hour, police had cleared the Zocalo, and much of the surrounding historic center, of virtually all protesters. Union organizers said they would reassemble away from the main plaza. The teachers have disrupted the center of one of the world's largest cities at least 15 times over the last two months, decrying a plan that aims to break union control of Mexico's dysfunctional education system. President Enrique Pena Nieto dashed the teachers' hopes of blocking the overhaul when he signed the new system into law Tuesday. On Wednesday, the protests began turning violent, as protesting teachers scuffled with riot police after officers set up a line to keep protesters from blocking one of the city's main expressways. City officials reported 15 police hurt as protesters seized some plastic riot shields from officers. They say they are now trying to maintain pressure to protect their rights and privileges as the government puts the labor reforms into effect and reduces union control over teacher hiring and assignment. As federal police helicopters swooped low overhead Friday, teachers struck tents they have been living in for weeks and burned garbage and plastic traffic barriers, filling the Zocalo with thick, acrid smoke. A group of battle-hardened teachers said clearing the tents was a tactical move to allow them maneuvering room for any possible clash. In echoes of the Oaxaca clashes of 2006, a group of Oaxaca teachers said they had already commandeered a bulldozer from road works in the Zocalo and had moved it to the front lines, to use against a possible police attack.