Isabel Lopez Torres, a shy-eyed 11-year-old, can't write her own name because she's never been to school. Like thousands of other children in Mexico, she's been barred from public schools because of a bureaucratic barrier: She has no birth certificate.

"I wish she had one," said Isabel's mother, Bertha Torres Castillo, who, like many poor people in Mexico, has never registered the births of her children. Standing in the doorway of her crumbling home in a shantytown next to the railroad tracks here, Torres held an infant in her arms as Isabel smiled from behind her skirt and her five other young children played nearby. "I want them to study, otherwise they'll all just be here taking care of babies," she said.

The government estimates that more than 5 million Mexicans lack birth certificates. For poor people in rural areas, getting a birth certificate can mean walking hours or even days to the nearest municipal office. For many, especially in the poorest indigenous communities, the $5 or $10 processing fee represents the family's food budget for a week.

This and other realities of poverty -- including broken families, alcohol or drug abuse, lack of education and mistrust of government -- leave many poor people unconcerned about bureaucratic formalities and unaware of the consequences of ignoring them. Not registering a child's birth has lifelong ripple effects: A birth certificate is required to obtain a voter-registration card or passport or to open a bank account. Lack of birth certificates has also been a problem for Mexican immigrants in the United States, who have no official form of identification.

"If you don't have a birth certificate, you don't have a legal identity," said Edmundo Lazos, an official in Chiapas state, which runs a program in conjunction with UNICEF to send officials into rural communities to identify children without birth certificates and issue them one on the spot. Similar programs are run in states such as Guerrero and Chihuahua, where officials have registered 47,000 indigenous people in rural communities in the past six years.

In recent decades, the problem has also spread to poor urban areas of such major cities as Guadalajara and Mexico City, fueled by massive internal migration. Millions of poor rural residents have moved to cities looking for work, putting those without birth certificates hundreds of miles from the hometown municipal offices that could issue them.

Mexico's constitution guarantees every child the right to public education. But principals and teachers routinely deny enrollment to students who cannot produce a birth certificate, education specialists here said, even though for many poor people that simple form can be as difficult to obtain as a college diploma.

"A 6-year-old kid in some village in the desert comes in without his documents, and the teachers don't let him in," said Carlos Ornelas, a leading education specialist. "It violates the constitution, but it happens all the time."

Torres, 42, who is unable to read or write, said her parents had no birth certificates and never bothered to get one for her, which makes it more complicated now to get them for her children. And, like many people struggling to feed their families, she wondered if it was worth the effort. Her husband, a bricklayer, supports their large family on less than $200 a month. She said that even if she managed to get all the children birth certificates and enrolled in school, seven sets of school uniforms, books, pencils and other items would be an unimaginable burden on their meager finances.

So illiteracy is passed down through the generations, remaining higher than 20 percent in some rural states. Of Mexico's 22 million school-age children, ages 5 to 14, more than 2 million don't attend any school, including at least 200,000 who aren't enrolled because they lack birth certificates, said Sylvia Ortega Salazar, head of public education in Mexico City. At a time when President Vicente Fox has said improving education is key to Mexico's progress, analysts said rigid bureaucratic regulations were another force holding the country back.

Marcela Gomez Zalce, a columnist for the Milenio newspaper, said Mexico's problem with bureaucracy extended beyond the birth certificate issue and was a drag on modernization. "If you want to open a business, or get a license plate or a telephone line or electricity, you need about 750,000 papers," she said. "It's bizarre, and it's nonsense. If we want to make this country better for the next generation, at least we should try to change this bureaucracy."

The bureaucracy that controls education in Mexico, the Ministry of Public Education, or SEP, is the largest in the Mexican government, with 1.5 million employees and an annual budget of $28 billion. It is widely seen as among the most tradition-bound and change-averse government agencies.

"It is a huge apparatus, designed by Kafka himself," said Ornelas, professor of education in Mexico City and author of a standard textbook, "The Mexican Education System." He said the system's rigid rules had not been modernized to keep pace with Mexico's needs -- including making exceptions to allow children without birth certificates to complete their education.

Ornelas said he saw the bureaucracy's rigidity firsthand a few years ago, when he accepted a job as an adviser to the education minister. "I had all these diplomas with my name on them," he said. "And what did they want? A copy of my birth certificate."

Ornelas said the ministry's cumbersome bureaucracy often discouraged principals and teachers from finding creative or compassionate solutions to problems. Many teachers, especially in remote rural areas, simply turn away children without birth certificates to avoid trouble with their superiors in the bureaucracy, he said.

Enrique Morales, an official in the education ministry, said it was reasonable to ask children to provide a birth certificate. The official ministry policy is to let children with no certificate finish the six years of primary school, he said, but not to be given credit: They are not eligible for the government form certifying that they completed primary school, which many employers require.

"A birth certificate is obligatory," Morales said. "Those are the rules."

"Yes, but why are those the rules?" said Jorge G. Castaneda, Fox's former foreign minister and an expert on Mexican education. "These rules probably had a reason many years ago. That reason has long ago disappeared, yet the rules remain the same. It doesn't make any sense to keep so many kids out of school for a bureaucratic reason."

Jose Guillermo Arechiga, chairman of an education committee in the lower house of Congress, agreed: "We need the education ministry to be more flexible, and the government needs to start programs to attend to these people. These rules limit a child's access to opportunities."

Torres's situation is typical of millions of working-poor families in Mexico. She lives in Colonia Ferrocarril, a warren of shacks alongside the railroad tracks here in Mexico's second-largest city. The family lives and sleeps in two small rooms, and the children play in a crumbling rooftop space.

Torres said getting her children birth certificates would be expensive and time-consuming. She would have to take a bus several hours to Colima and would need to hire a lawyer to help straighten out the paperwork. She figured it could cost her husband more than a month's salary and could take two or three weeks.

"I couldn't go for more than a day," she said. "Who would take care of my children?"

Ana Ontiveros Casian, who works for the city's social welfare department, said she and other social workers spend huge amounts of time and effort trying to get birth certificates for people in neighborhoods such as Colonia Ferrocarril. But the task was often daunting, she said, because there are so many broken families and confusing family histories.

Isabel and four of Torres's other children attend regular open-air classes given by Ontiveros and other government teachers who come to the neighborhood several times a week, part of an outreach program to help children not enrolled in public schools. They don't require birth certificates.

Ontiveros said Isabel is too far behind in her studies to ever attend a regular school. But she said when the girl turns 14, if she masters basic reading and writing, she could enroll in a state vocational program to learn a trade, perhaps as a hairdresser or day-care worker.

"But to get into that program," Ontiveros said, "she needs a birth certificate."

Bertha Torres Castillo's seven children, including Isabel, 11, left, Jonathan, 9, on floor, and Vanessa, 6, are not permitted to attend school in Mexico because they lack birth certificates.Jovanna Lopez Torres, 3, left, plays at home. Like her siblings, she will not attend school because she does not have a birth certificate. An estimated 5 million Mexicans lack the document, also required to vote, bank or get a passport.