So poor was the education she received at her public high school, Pilar Vega Martinez had to take an extra year to study for the Prueba de Selección Universitaria — the Chilean version of the SAT.

The work paid off. Her score on the exam was good enough to get her into the top-rated University of Chile. Vega is now in her third year, studying to be a nurse. And thanks to an important change in government policy, life got easier after that: She didn't have to pay.

That's because Chile has made college tuition-free — through a policy called gratuidad — after years of angry public protests about escalating tuition and student loan debt and the gulf in quality between the institutions attended by the wealthiest and the poorest students.

It's a version of "free college" along the lines of what many in the United States are talking about — including several Democratic candidates for president.

Chile's educational system has significant parallels with that of the U.S.: a robust sector of private colleges alongside public universities; high college tuition; and, before gratuidad, significant student loan debt.

That makes it a prime test case for the American version of the idea.

Among other things, what has happened in Chile proves that free tuition is politically popular.

In 2013, Michelle Bachelet, then the socialist candidate for president, made it a centerpiece of her campaign and won by a 2-to-1 margin; several years later, the Chilean Congress passed it by a vote of 92-2. Sebastián Piñera, the conservative who succeeded Bachelet, has continued the policy.

And it's a popular idea in the U.S., too: Seventy-one percent of Americans support free tuition at public universities or colleges for students who are academically qualified, according to a survey by PSB Research for the Campaign for Free College Tuition.

How it came to be

A driving force behind the move to gratuidad in Chile was deep socioeconomic divisions in society, a remnant of Chile's authoritarian government that ruled the country from 1973 to 1990.

In 2011, the frustrations and anger boiled over into strikes and protests. Demonstrators marched against high college costs and large amounts of personal debt from student loans.

The frustrations then were similar to those that have sparked political protests in recent weeks.

"In Chile, you can't move things" without people in the streets explains Miguel Crispi, who is now a deputy, or member, of the Chilean Congress.

Back in 2011, the debate was all about education.

Chileans, over their breakfasts, "were talking about inequality," says Crispi, who was a student leader during those protests. He recalls whole families "talking about, 'How can we afford a higher education? Is it fair to go into debt for studying?' "

As in the U.S., the movement rose above financial concerns about paying for college to a broader, philosophical principle: Higher education is a right.

"The most important way of being free is having the tools for doing what you want to do in life. That's education," says Crispi. "It's about being free or having the chance to be free."

It's expensive

When gratuidad finally began in Chile, lawmakers quickly realized that the ambitious program — free tuition for everyone — costs a lot, even in a country with just over 5% the population of the U.S. It became clear the program had to be scaled down and delayed, with complex restrictions added.

The same thing has happened to free-college proposals in the U.S.: A campaign promise by New Jersey Gov. Phil Murphy to make community college in that state tuition-free, for instance, had to be reduced to a pilot program. And the free-tuition plan in New York state set an income limit for recipients.

In Chile, the biggest cost-saving measure was reducing the number of students who qualified. College would not be free for everyone but for the poorest Chileans — only those whose families were in the bottom half of the income range.

Gratuidad has since been expanded to include the bottom 60%. Even after those revisions, the price tag for Chilean taxpayers is $1.5 billion a year. (In the U.S., Sen. Bernie Sanders' plan to make two- and four-year college free for everyone — regardless of income — is projected to cost the government $47 billion per year.)

Is it working?

Despite the investment in Chile, the reform is making only slow progress toward its primary goal: expanding access to higher education for the lowest-income students. That's because nearly 90% of those low-income students already had financial aid before gratuidad.

But looked at another way, the prospect of free tuition does inspire students to enroll in college who might not have considered it previously. A recent report found that 15% of Chilean students in the program would have otherwise not sought a college education. And Chileans who get free tuition are also slightly less likely to drop out than their classmates who don't, the government has found.

"For some families, the assurance that they are not going to be facing any payment at all makes a difference in their willingness to take the chance and have their kid apply," says Andrés Bernasconi, a professor at the Pontifical Catholic University of Chile who studies gratuidad.

When Pedro Córdova Guerra, 55, was growing up in the suburbs of Santiago, he didn't even let himself dream about college. His family was poor, and in his mind, college was only for the wealthy. "Back in my time, there were no opportunities," he says. "I used to be bitter that I didn't get a chance to go to school. It was very difficult."

He says he lived through that big shift in thinking: "There were new ideals around education. ... We expect it to be a right."

And his children are living that ideal. His middle daughter, Verónica Córdova Freire, is using gratuidad to study mechanical engineering at the University of Santiago.

But even with free tuition, Verónica tells us she is still struggling financially. To save money, she lives at home with her parents and two siblings.

She rides a bus to campus, which takes about 2 1/2 hours each day. "That's two hours I'm not sleeping, not studying," she says. Her school helps pay for lunch, but it's not enough; she eats most meals at home with her family.

Many students we talked with face the same challenges. Gratuidad doesn't cover other costs, including rent, food, books and transportation.

Most free-tuition programs in the U.S. don't cover those expenses either. And because they don't, two of the most ambitious programs, in Tennessee and New York state, have failed to improve affordability for low-income students, according to a report by the Institute for Higher Education Policy.

In fact, that report found, in Tennessee it was higher-income students who benefited, getting an average of nearly $1,500 each to help them pay for college educations their families could already afford.

The length it covers

Beyond the financial limitations, however, students in Chile have another big complaint about gratuidad: the time limit. The program requires students to complete their degrees, or courses of study, on time. For example, a traditional four-year degree must be completed in that time.

One expert likened it to a time bomb and, sure enough, this year 27,000 of the students who had been enjoying free tuition came to the end of their eligibility before they graduated, according to the University of Chile Student Federation Research Center.

Pilar Vega Martinez, who is in her third year of studying to be a nurse, says that last year she got bronchitis and missed weeks of school. "I was doing really well," she says, but now, it will take her longer to finish than gratuidad will pay for.

"I'm still thinking about how I'm going to pay for that last year," she says in Spanish during a study break in the university's library. "I've had to work while studying to start saving money."

Students in Chile take 10% to 30% longer than the prescribed time, on average, to finish their degrees, the government says. That mirrors what happens in the United States, where many students need, for example, five or six years or more to complete a bachelor's degree.

"In 2011 the principal problem was that gratuidad didn't exist," says Ximena Donoso Rochabrunt, who just finished law school and is studying for the equivalent of the bar exam. "And people are still mad that its existence is only partial."

The impact on private universities

Private colleges in Chile, which can participate in gratuidad if they choose, are facing a financial squeeze because the government limits the tuition they can charge. In the first year, only a few private institutions took part, since they have relatively high tuition and serve wealthier students whose families' incomes are too high to qualify anyway.

For those institutions that do sign on, "costs are going to go up and income is going to stay very still," says Claudio Ruff, rector of the private Universidad Bernardo O'Higgins and president of the national association of private universities. His office overlooks a grassy quad, with a portrait of O'Higgins, the 19th century Chilean independence leader, on the wall and opera music playing in the background.

Already, Ruff says, 15 private universities and colleges have closed or are in the process of closing because it's hard to compete with "free."

Schools like his that remain but have opted out of gratuidad are cutting money-losing programs, offering discounts and scholarships and adding research to attract more students, including international ones.

The colleges have largely themselves to blame for this predicament, argues Luis Felipe Jiménez Leighton, an economist and former adviser to the Education Ministry who helped negotiate gratuidad. Their high fees helped drive the protests that resulted in the free-tuition system.

"Fat cats," he called them. "Now [they] have to get lean. And that's a consequence of gratuidad that we didn't intend, but it's a byproduct and to some extent it's a welcome byproduct."

Some private institutions in Chile may have gotten fat, concedes Ruff. "But not any more. Private universities spend more money [than public ones], but they spend it better." Besides, he adds, private universities can "tighten their belts faster."

Looking ahead

As it stands now, gratuidad is set to expand if and when tax revenues allow. But the argument in Chile now is over whether it should.

Three years in, has it been worth it? Many, like Rosa Devés, say yes. Devés is a vice president for academic affairs at the University of Chile.

When some people ask "why am I going to pay for a rich person to go to university?" her answer is: "You're not paying for the rich person. You're paying for the institution that will have all the representation of the society in it."

But Chile simply may not be able to afford that, says Leighton, the economist. "We're not in a state of abundance where we can finance everything," he says. "You have to prioritize some things and in the process to leave somebody in and somebody out."

Right now, 68% of Chileans say they are against extending free tuition to everyone, preferring that only people in the bottom 70% of income be covered, one poll found.

Conservatives, who now hold a majority in government, would prefer to put more money into primary and secondary education, where inequalities grow.

"Free tuition is not the only solution for getting more vulnerable students into university or into higher education," notes Jaime Bellolio, a conservative deputy in Congress who serves on the education committee. Regardless of free tuition, he explains, students still need the academic preparation if they are to gain admission into top universities.

"If you want to have more vulnerable students in good universities and good professional institutes you have to level up the quality of education before they come."

He acknowledges that this point is not as politically catchy as "free tuition": "It's not as good for the elections, but it is better for the long run, and it's better public policy. Those first years are the ones that make all the difference."

Still, Devés argues that Chile has made big steps forward since Chileans took to the streets eight years ago.

"The path is not perfect," she says, pulling out a copy of the actual statute. Devés helped write the law and has highlighted some of her favorite parts. She tears up as she reads the words aloud. Translated from Spanish:

"The law establishes that higher education is right, that should be within reach of all people, in accord with their abilities and merits."

"I feel quite proud," she says. "It may be just words, but still, they are the correct words."

The work isn't finished yet, she adds, but gratuidad is "a very important starting point."

This story about tuition-free colleges was produced in collaboration with The Hechinger Report, a nonprofit, independent news organization focused on inequality and innovation in education.