MEXICO CITY — Riot police swept thousands of striking teachers out of the heart of Mexico City on Friday, driving protesters through the streets with tear gas and water cannons in a swift end to the weeks-long occupation of the Zocalo plaza over reforms to the dysfunctional national education system.
It was a dramatic reassertion of state authority after weeks of near-constant disruption in the center of one of the world's largest cities. The teachers have marched through the capital at least 15 times over the last two months, decrying President Enrique Pena Nieto's plan to break union control of education with a new system of standardized teacher testing that become law on Tuesday.
Authorities did not immediately report any injuries. Federal police chief Manuel Mondragon said more than 20 demonstrators were arrested.
The teachers' demonstrations have slowed passage of Pena Nieto's education reform and the pace of his wider agenda of structural reforms, which seeks to reengineer some of Mexico's worst-run institutions, including the weak tax-collection system and underperforming state oil company.
Pena Nieto will almost certainly gain significant political capital if the Friday afternoon operation, led by federal instead of city police, definitively ends the demonstrations that have snarled traffic for weeks in Mexico City.
There was additional pressure to clear the Zocalo where the teachers had been camping out before the president's first traditional Independence Day celebration in the massive colonial-era square on Sunday and Monday.
The confrontation erupted after the teachers armed themselves with metal pipes and wooden and blocked off the Zocalo with steel grates and plastic traffic dividers, threatening to scuttle the Independence Day gathering.
The government responded that celebrations, including the president's shout of independence from a balcony of the National Palace overlooking the Zocalo, would take place in the square as scheduled on Sunday night. 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 similar battles with police in poor southern states, said they would not move from the square where they have camped out since last month. Some fixed knives and nails to wooden planks and declared themselves ready to fight. Others set up sewage-filled portable toilets in the path of police vehicles.
Shortly after 4 p.m., the police swarmed in, shooting tear gas canisters and spraying water from armored trucks. Protesters hurled sticks and chunks of pavement broken from the streets around world-famous tourist attractions including the Metropolitan Cathedral, the Templo Mayor and the National Palace.
But within a half hour, police had cleared the Zocalo and much of the surrounding historic center of virtually all demonstrators. Union organizers said they would reassemble away from the main plaza at the nearby Monument to the Revolution. Small knots of teachers, self-described local anarchists and other supporters hurled bottles and rocks at police on some of the main avenues of downtown Mexico City.
"We're going to reorganize and go back," said a masked teacher who would only give first name, Juan Carlos, as he waited in an alley with about 10 other demonstrators. "It's not going to stay like this. The government isn't going to repress us."
Pena Nieto's new standardized system of test-based hiring and promotion would give the government the tools to break teachers unions' near-total control of school staffing. That control includes the corrupt sale and inheritance of teaching jobs, and it has been widely blamed for much of the poor performance of Mexican schools, which have higher relative costs and worse results than any other in the 34-nation Organization for Economic Cooperation and Development.
With the education reforms now law, the teachers say they are trying to maintain pressure to protect their rights and privileges as the government puts the changes into effect and reduces union control over teacher hiring and assignment.
The protests were being led by the National Education Workers Coordinating Committee, or CNTE, the smaller of the country's two main teachers unions. The larger union has supported Pena Nieto's reform.
The teachers argue that because they are from poor states and don't have the means to enact peaceful change, their main strength is the ability to shut schools and make life inconvenient in Mexico's economic, political and cultural heart.
Many independent observers say that the teachers are simply accustomed to using disruption as a tactic for winning concessions like better pay and benefits from the weak governments of the states where teachers are among the most powerful political forces.
Mexico City's government avoided intervening until Friday, increasing the frustrations of many capital dwellers. The city's leftist government has historically been slow to crack down on demonstrations, fearful of violence on the capital's streets. Adding to the aversion to force is the legacy of two massacres of protesting students in 1968 and 1971 that became national traumas.
On Wednesday, the demonstrations began turning violent, as demonstrating teachers scuffled with riot police after officers set up a line to keep them from blocking one of the city's main expressways. City officials reported 15 police hurt as teachers seized some plastic riot shields from officers.
Michael Weissenstein and E. Eduardo Castillo contributed to this report.
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