Easter vacation was over, but there wasn't a teacher in sight at the boarding school for indigenous children on the edge of this sunbaked southern Mexico hill town.

A 37-year-old cook who hadn't finished high school sat between two little girls on a cement stoop outside the kitchen, peering at their dog-eared notebooks as they struggled with the alphabet and basic multiplication.

"I've got the children here. If there aren't any classes while they're here, I have to teach them," said the cook, who shared only her first name, Gudelia, for fear of retaliation from striking teachers.

A short drive away, teachers marched by the thousands through the streets of the state capital, some masked and brandishing metal bars and sticks in an escalating showdown over education reform that's become a key test of President Enrique Pena Nieto's sweeping project to reform Mexico's most dysfunctional institutions.

The fight is dominating headlines in Mexico and freezing progress on a national education reform that Pena Nieto hoped would build momentum toward more controversial changes. Those include opening the state-owned oil company to foreign and private investment and broadening Mexico's tax base, potentially with the first-ever sales tax on food and medicine.

Pena Nieto's first major legislative victory after taking office in December was a constitutional amendment eliminating Mexico's decades-old practice of buying and selling teaching jobs, and replacing it with a standardized national teaching test. That's heresy to a radical splinter union of elementary and high-school teachers in Guerrero, one of the country's poorest and worst-educated states. The teachers claim the test is a plot to fire them in mass as a step toward privatizing education, although there is little evidence the government plans that.

Reform advocates say the dissidents simply fear losing control over the state education system and the income it provides, despite the need to reform a system that eats up more of the budget and produces worse results than virtually any other in the world's largest economies.

The 20,000-member group walked out more than a month ago, turning hundreds of thousands of children out of class. Then it launched an increasingly disruptive string of protests.

On Wednesday, the protesters won support from a wing of the armed vigilante groups that have multiplied across poor Mexican states in recent months. On Thursday, they blocked the main highway from Mexico City to Acapulco for at least the third time, backing up traffic for hours. On Friday, they shut down entrances to some of the biggest stores in the state capital.

After returning Mexico's former ruling party to power, Pena Nieto won international acclaim in his first five months by taking on some of the country's most powerful people. He jailed the head of the far-larger national teacher's union when she threatened to fight school reform. Then his push to open the telecommunications business provoked a multi-billion-dollar drop in the stock of the market-dominating phone companies owned by the world's richest man.

Now the president finds himself facing unexpectedly tough resistance from rural teachers in straw hats and plastic sandals in his first direct conflict with the Mexican far left, a diverse and fractious group encompassing student activists, militant unions, anarchists and the remnants of indigenous guerrilla groups. The dissident teachers and their growing list of allies say that more protests are planned for other poor and heavily indigenous states starting Monday.

"If it spreads into other states then it's a real problem. It means the government can't just plan on pushing the agenda from the top," said Federico Estevez, a political science professor at the Autonomous Technological Institute of Mexico.

The conflict is fueled by the importance of teaching jobs for the poor mountain and coastal villages where the dissident union is strongest. Teaching jobs in Guerrero with lifelong job security, benefits and pension pay about $495 and $1,650 a month, depending on qualifications and tenure, well above average in rural areas, according to teachers and outside experts. They said the price to get such as job can cost as much as $20,000, usually going to the departing teacher, with cuts for union and state officials.

State education officials declined repeated requests for comment.

Only 47 percent of Mexican children graduate from the equivalent of high school, even though the country spends as greater share of its budget on education than any other member of the 34-nation Organization for Economic Cooperation and Development except New Zealand.

Teachers at schools that in Guerrero this week told The Associated Press that they agreed for the need for reform, but pointed to a host of problems unrelated to teacher qualifications, including class sizes of up to 40 students per class, curricula that promote rote learning over engagement and a lack of state money for maintenance that forces parents to contribute a mandatory $25 fee so that schools can pay for costs like classroom fans and fixing sports fields.

As he marched with the dissident union on Wednesday, Brutilio Tapia Cande, a 26-year veteran teacher from a town deep in the Guerrero highlands, denied that jobs were sold but said he saw nothing wrong with the tradition of passing a steady lifelong income on to his children.

"It's a source of income for the highlands and for the whole state," he said. "The teachers are the ones who feed the highlands.

"If a teacher retires his place automatically is inherited by his son," Tapia continued. "But now what the government wants is just to fire and cut the budget."

But there are signs of waning sympathies even among the residents of the towns that depend so heavily on teachers' income.

One is Ines Sanchez, whose 8-year-old Guadalupe chased her friends and a few stray sheep among the closed classrooms of the Lazaro Cardenas Primary School in Atliaca this week as her teachers protested in the capital.

"We parents feel bad because the children aren't going to school, they aren't learning anything," Sanchez said. "When the time comes to go back to school they don't want to, because they're used to just running around playing."

So far there's no resolution in sight.

The government has deployed hundreds of unarmed federal police to unblock the highway, a goal police commanders have accomplished through negotiation and one clash that left a handful on both sides injured. Pena Nieto has said little about the conflict, but there is increasingly tough talk coming from his top aides.

"We're not going to respond to the threats that they've been making," Interior Secretary Miguel Angel Osorio Chong, Mexico's top law-enforcement official, said Friday. "We believe there are limits and the limit is the rule of law."

Gonzalo Juarez Ocampo, the most visible leader of the State Coordinator of Guerrero Education Workers, also issued an unsubtle warning of potential violence on Wednesday when he announced the union alliance with the 1,200-member vigilante group known as the Regional Coordinator of Community Authorities. That had ominous overtones in a country where teacher's protests exploded into clashes with police in 2006, shutting down the city of Oaxaca for five months and leaving at least a dozen dead.

The new movement, Juarez said, is "peaceful, a citizen's movement, a legal movement."

"We hope that the government understands that, and we don't have to move to a different phase," he said.


Michael Weissenstein on Twitter: http://Twitter.com/mweissenstein


Jose Antonio Rivera contributed to this report.