Mexico City, Mexico — As most of Mexico's 26 million students return to school this week, more than two million remain at home after teachers launched strikes to protest reforms aimed at improving the country's woeful public education system.

The strikers shut down some 24,000 schools in five impoverished states across southern Mexico, including the violence-plagued Pacific Coast state of Michoacan, in pursuit of a host of demands. Chief among them was a call for cancellation of new federal regulations requiring teachers to take competency exams to be hired and retained. More than 1,500 teachers idled 500,000 other students in the Gulf Coast state of Tabasco to force the resignation of the state's education minister.

Some 20,000 strikers poured into Mexico City on Monday to besiege the National Congress and set up camp in the sprawling central plaza, where leaders say they will stay indefinitely. Hundreds trying to force their way into a session of legislators voting on reforms fought with riot police outside the congress building, smashing cars, and injuring twenty-two officers.

At the behest of President Enrique Peña Nieto, congress passed sweeping educational reforms last December. Legislators this month have been negotiating secondary legislation to put the reforms into effect.

"Education is the most powerful instrument for Mexicans to reach new and better opportunities in life," Peña Nieto, as classes began and strikers entered Mexico City.

The striking teachers say they are being used as scapegoats for the real problem: years of inadequate budgets and endemic corruption that have made Mexico's among the worst public education systems in the industrialized world.

"We want the whole national education system to be evaluated," strike leader Juan Jose Ortega told the Mexican press on Monday.

A generation ago most Mexican adults were lucky to finish six years of grade school. Today, practically every Mexican child 15 years old and younger is in school, according to the Organization for Economic Cooperation and Development. But the quality of education varies dramatically. Mexico leads the Organization for Economic Cooperation and Development's (OECD) 34 member nations in dropouts, with less than half the students who begin eventually earning a diploma.

Federal police jailed Elba Esther Gordillo, the powerful boss of the National Education Workers Syndicate, or SNTE, the largest teachers' union, in February on corruption charges, removing a powerful political obstacle to the reforms. Despite reportedly living on her teacher and union salaries, Gordillo amassed a fortune worth millions of dollars in her more than two decades in control of the 1.2-million member syndicate.

Gordillo's arrest and replacement with an underling subdued the giant union. The strikes this week are being led by the National Education Workers Coordinator, a rival and often more radical union to the larger SNTE. But among the more radical strikers are those of the SNTE's Section 22, which maintains a grip on public education in Oaxaca state. Section 22 launches crippling strikes in the state nearly every spring, pushing for sometimes trifling wage increases and other benefits.

The teachers throughout southern Mexico have been fighting against the reforms all year, marching on Mexico City, striking at home, and fighting with state officials. Rioting teachers attacked and burned government and political party offices in the Guerrero state capital of Chilpanincingo in April after legislators approved the reforms.