TIJUANA, Mexico - Weekday mornings at 5, when the lights on distant hillsides across the border still twinkle in the blackness, Martha, a high school senior, begins her arduous three-hour commute to school.
She unlocks the security gate guarded by the family Doberman and waits in the glare of the Pemex filling station for the bus to the border.
Her fellow passengers, grown men with their arms folded, jostle her in their sleep.
Martha's destination, along with dozens of young friends - U.S. citizens all living in "TJ," as they call their city - is a public high school eight miles away in Chula Vista, Calif., where they were born and where they still claim to live.
Martha and her friends stand for hours in a human chain of 16,000, cell phones in one hand and notebooks in the other, as they wait to cross the world's busiest international land border on foot, fearing delays that could force them to miss a social studies final.
In San Ysidro, the port of entry, they board a red trolley to another bus that takes them to school. They are sweating the clock - the bell rings at 8 a.m. sharp.
"Most of the time I am really, really tired," said Martha, whose parents moved back to Tijuana because the cost of living was cheaper than in southern California.
"I try to do my best," she added. "But sometimes, I just can't."
In the raging debate over immigration, almost all sides have come to agree on tougher enforcement at the border.
But nearly unnoticed, frustration is focusing locally on border-crossers who are not illegal immigrants but young U.S. citizens whose families have returned to Mexico yet want their children to attend U.S. schools.
El Paso students
Called "transfronterizos," these students migrate between two cultures, two languages and two nations every day, straining the resources of public school districts and sparking debate among educators and sociologists over whether it is in U.S. interests that they be taught in the United States.
Although some Mexican families pay the steep tuition required of out-of-district students, most do not, and many do not pay property taxes that support public services.
Although their exact numbers are unknown, their presence reflects the daily complexities of border life - among them, economic and educational disparities between the United States and Mexico and families splintered by deportation and unemployment.
Transfronterizos can be found from Calexico, Calif., to El Paso, Texas, where violence in neighboring Juárez has led to the creation of a designated lane for 800 to 1,400 students daily, including U.S. citizens who attend El Paso schools.
Martha's family pitches in on the mortgage for a Chula Vista house, where members of the extended family live, and pays utilities to establish residency.
Other Tijuana families rent apartments, "borrow" fake addresses from friends or create a post office box. Sometimes a relative in the district is appointed their child's legal guardian.
"It's stressful," Martha says of the house that is not really her home. "You can get found out and kicked out of school. Sometimes I feel bad for lying. But I'm just going to school."
Although educational outcomes have greatly improved in Mexico, low high school graduation rates and high attrition rates in the northern industrial states of Baja California and Chihuahua "hinder development of a highly educated workforce," concluded a 1997 study by the Trans-Border Institute at the University of San Diego.
"The gap between the U.S. and Mexican sides is great enough that people have a strong incentive" to cross, said David Shirk, the institute's director.
For educators, determining whether a student meets residency requirements can be a thorny task, with rules varying from district to district and state to state.
In San Ysidro, families must provide a mortgage or rental agreement and show utility bills in their name.
Over the past two years the district has sent "letters of exclusion" to more than 20 families. In some cases, fraudulent documents were discovered.
Manuel H. Paul, the superintendent, said educators were attuned to "red flags" like a phone call from a school nurse that reaches a disconnected number.
"The student will say, ‘We live in Tijuana,"' Paul said. "Children most of the time don't lie."
Supreme Court ruling
In 1982, the Supreme Court established that schools cannot inquire about a family's immigration status. Ed Brand, superintendent of Sweetwater Union High School District in Chula Vista, says a U.S. citizen living outside the county would pay tuition of $7,162.
"We're not the INS," he added, referring to the former Immigration and Naturalization Service. "Can one get by us? I imagine one can."
The issue is fairness, whether a student lives in Mexico or just outside a preferred school district in the United States, argues Steven A. Camarota, the research director for the Center for Immigration Studies in Washington, which favors limits on immigration.
The possibility that these individuals could "pay enough in taxes to cover the costs of consumption of public services is basically zero," he said.
Martha and her friends view classmates who live in the district as coddled couch potatoes.
They don't have to deal with jeering workers at the border cussing them for cutting in line.
Or say "wake me up" to the Tijuana taxi driver who drives them home after dark.
One teacher in Chula Vista, whose name was withheld to protect students in his class, including Martha, said, "I can't draw all I want from her. Her intelligence is hidden away by her tiredness."
Yet teachers and guidance counselors say that despite the academic challenges, students who get up at 4 a.m. to be at school show signs of becoming resilient leaders.
"They know who are they are and what they want," the teacher observed.
"They're not going to be working at Jack in the Box. They're go-getters."