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 weekslong occupation of the Zocalo plaza over overhauls 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 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 Mr. Pena Nieto's education overhaul and the pace of his wider agenda of structural overhauls, which seeks to re-engineer some of Mexico's worst-run institutions, including the weak tax-collection system and underperforming state oil company.
Mr. 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 Sunday and Monday.
The confrontation erupted after the teachers armed themselves with metal pipes 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 Sunday night.
Mr. 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 overhauls 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, the smaller of the country's two main teachers unions. The larger union has supported Mr. Pena Nieto's overhaul.