Columbus, New Mexico (CNN) Fifth grader JoAnna Rodriguez is on her way to the school bus when she realizes she's forgotten something important. It's not homework or lunch. She pulls out a cell phone and calls home while rummaging through her horse-themed backpack.

"Mom, I forgot my passport," she says.

JoAnna, 11, needs proof that she is a US citizen to get to school. The self-proclaimed future nurse with the long braid draped down one shoulder is one of nearly 800 American students who live in Palomas, Mexico, and cross the US border each morning to attend public school in nearby Columbus.

For more than four decades, New Mexico's state constitution has guaranteed American citizens a free education, no matter where they live. It gives families dealing with deportation an opportunity to live together in Mexico, without sacrificing their children's education in the US. And it's created scenes like this one at a border-crossing checkpoint.

According to U.S. Customs and Protection, hundreds of students cross other parts of the US-Mexico border to attend school in places like El Paso, Texas. For those students, however, the American education is not free. They pay to go to private schools.

By 8 a.m., a line of with fidgety children carrying donuts and hot chocolate stretches out the door at the US Customs and Border Protection Columbus Port of Entry, where agents tease students while swiping passports and inspecting belongings. They flip through notebooks, open lunch boxes and ask questions.

"What's in your bag?" an agent asks.

"Candy," replies a hazel-eyed girl in a pink glittery shirt.

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As children cross the border into New Mexico, mothers back in Mexico stand on tiptoes to wave goodbye. Many of these kids' parents were deported and are not allowed to pass beyond the barrier that has become a way of life here.

The bollard fence dividing the two towns marks the border, but it hasn't kept the two countries' cultures from seeping through the fence. You'll find tacos and hamburgers sold on both sides. Streets are lined with vendors advertising in English and Spanish, and American pop and Mexican Norteño music can be heard from cars in Columbus and Palomas.

Each morning, buses wait on the US side to shuttle the students north for an education in the United States of America.

It's a five-mile bus ride. So close, and yet for some of their parents, so far.

The Rodriguez family

JoAnna's dad, Jesus Rodriguez, is a broad-shouldered mechanic with a soft, raspy voice. He is an optimist, and loves animals and the countryside.

Her mother, Arianna Rodriguez, works with special education students. She is nurturing, outgoing, and the rock of the family.

There is another big difference.

Mom is a US citizen. Dad is not.

Jesus, 35, was born and raised in Zacatecas, Mexico. He was kicked out of the US in 2007 after being caught crossing the border illegally several times.

For Arianna, 30, it's not easy to explain their complex situation to her daughters, JoAnna and her younger sister Nahima, 10.

"Dad broke the law because he went in multiple times to the States. That's why he had to wait," she tells them. "The law is the law and we have to follow it."

I feel sad that our graduation is coming up and my dad isn't going to be able to come. JoAnna Rodriguez

JoAnna fights back tears when talking about her father. Nahima is concerned for their dad, too. The shy fourth grader worries that new immigration policies under President Trump could hurt her father's chances to get back into the US.

"I'm scared," she says, while answering questions on the playground at school.

After Jesus was deported 10 years ago, he moved to a border town in Chihuahua, Mexico, where he had relatives. Unwilling to give up opportunities in the US for their children, he and Arianna agreed that she and their daughters would remain in Hatch, New Mexico.

The decision forced the family to separate for five years. On weekends, Arianna drove two hours south with the girls to Ciudad Juarez to visit Jesus. When it was time to leave Mexico, JoAnna would beg her mother to let her stay with her father.

"She would tell me, 'Don't tell mom where I'm hiding,'" Jesus says.

Arianna described the weekend trips as a painful and impractical ordeal. She worried her children were missing too many special moments with their father.

"Giving dad a goodnight kiss, losing their first tooth, walking, talking ... those are the moments that he was missing," she says, her voice choking with emotion. "I would have loved for him to be there."

'A silver lining'

When Arianna first heard about an elementary school in New Mexico educating US citizens living in Mexico, she was skeptical. It seemed too good to be true.

So she took a tour of Columbus Elementary School. Three days later, she moved to Palomas with the two girls. Jesus met them there.

"There is always a silver lining," says Columbus Elementary Principal Armando Chavez. "This school is the silver lining."

I worry about the longevity of this school. Columbus Elementary Principal Armando Chavez

Two-thirds of the 700 students attending Columbus Elementary live in Palomas, according to Chavez. They are US citizens.

"You must have a no-excuses mentality if you're going to lead this school," Chavez says. "Kids come in with pretty extreme cases."

Enrollment also is growing, and Chavez is concerned about keeping up with the influx of new students.

"I worry about the longevity of this school," he admits.

The school, which offers a bilingual education, has three rules posted in every classroom: Show respect, make good decisions and solve problems.

While students in one first-grade class write sentences in English, a second-grade class down the hall focuses on grammar in Spanish. Every morning children pledge allegiance to the American flag in both languages.

At lunch, JoAnna talks to five friends in English. Two the girls live in Palomas, the other three in Columbus.

"We usually talk about what we're going to play outside, and secrets," she says with grin. "But I can't tell you."

This border situation is not unique. Schools near the border in other states, like Texas and California, provide an education for students living in Mexico, but not for free. They're mostly private, and most families can't afford them.

Not everyone in Columbus supports the arrangement that brings students from Mexico, however.

Keith Harris, First Vice-Chair of the Luna County Republican Party, understands that children who are US citizens deserve an education in Columbus. But he's not sure it should be free.

"They're getting free tuition while other parents are paying taxes," he says.

Looking to the future

The Rodriguez family hopes they can count on the school to keep them together. Despite the hardships presented by Jesus's deportation, they have learned to appreciate living under the same roof.

They have a new addition, a baby girl named Sophia. And they dream about simple things.

"We talk about going to Walmart together, us four -- well, us five," Arianna says. "It's just like the simplest thing you think could think about."

Even though the school gives the Rodriguez family the opportunity to live together, Jesus is still missing special moments in his daughter's lives because of his immigration status.

God squeezes, but he doesn't choke. Jesus Rodriguez

"I feel sad that our graduation is coming up and my dad isn't going to be able to come," JoAnna says.

Jesus Rodriguez has waited 10 years for his turn to pursue a legal way back to the US. But he and his family fear President Trump's strict immigration policies will quash their dreams.

The family has hired an immigration attorney from El Paso, and Jesus has applied to become a legal US resident.

"Yes, it worries me, but I leave it to God. I've learned that leaving things to God, things go the way they're supposed to go," Arianna says.

With a tear streaming down his face, Jesus explains he is relying on the same faith.

"God squeezes, but he doesn't choke," he says. "I know he will help us."

Each afternoon, Jesus returns to the border he can not cross to pick up his girls after school. After Mexican border officials scan the students' backpacks, the two sisters race each other to dad's truck, hoping to claim the prized front seat. JoAnna wins.

Jesus smiles, knowing he's going back to a home where his family lives together.