MEXICO CITY, Mexico — Some 26 million children and young adults hit the books again in Mexico, striving against the odds for the education they desperately want.

Despite decent grades and years of hard work, Victor Mendez, 19, likely won't be among them.

He's one of hundreds of thousands of high school graduates turned away this summer from the country's overwhelmed public universities. The schools are so crowded, admissions have been restricted to those students with the highest grades and entrance exam scores. And private universities, prohibitively expensive for most families and often of terrible quality, are an option for few.

Like Mendez, whose father is a street vendor in a dusty, poor town on Mexico City's eastern fringe, many of the public university “rejects” hail from the gritty working-class barrios and slumping rural villages where most Mexicans live. They're often the first in their families to climb within reach of a university degree. Now they're being told not to bother.

"It's very important for me to be able to get ahead, for the country to grow socially and economically," Mendez said. "But they exclude you more every time."

For several decades, a succession of Mexican presidents has pushed to improve the country’s glaringly inadequate public education system. To the fury of powerful unions, President Enrique Peña Nieto and legislators are fine tuning reforms that would, among other things, force teachers to pass exams to keep their jobs. Striking teachers have idled 2 million students in four Mexican states.

Most Mexicans of a generation ago, especially the poor majority, were lucky to finish six years of grade school. Today, virtually every Mexican child up to age 14 is studying, according to the Organization for Economic Cooperation and Development. Still, only half of Mexico’s current primary school students are expected to earn high school diplomas, the OECD estimates. Little more than a quarter will study beyond that.

Mexico this year ranks first among the 34 OECD countries for high school dropouts and last in the percentage of students seeking bachelor’s degrees. Only 12 percent of Mexicans in their 20s are studying, less than half the OECD average.

"They've cut short the dreams of so many of us,” said street vendor Jaime Acosta, 28, who finished high school at 22 and still hopes to enter university despite being rejected four times.

"It's a constitutional right that's not being fulfilled," said taco vendor Arturo Espinal, 50, whose daughter was among thousands turned away this year by Mexico City's mammoth National Autonomous University, UNAM, ranked as the second best public university in Latin America. "The government officials say youths are the future of Mexico and then they leave them in the street."

Mexico's population has surged by more than half in three decades, to 118 million, jamming far more workers into the economy than it can absorb.

Many university graduates face despairingly low salaries and slow advancement even if they're able to land jobs in their chosen fields. But those lacking a degree too often face lives of dead-end labor paying $100 a week at best.

“The minimum wage lets you just live day to day,” said Dalia Flores, 21, 3 1/2 years into a five-year urban planning major at UNAM, which has more than 300,000 students enrolled across several campuses and a network of high schools. “We are studying so we don't face that.”

With a university-educated father recently retired from a government career, Flores counts herself among Mexico's lucky few. As a graduate of one of UNAM's prep schools, she had admission preference to the university over outsiders like Mendez.

With a degree, a career with Mexico City's government is almost guaranteed, paying a wage that will allow her to have her own home, a car, a life.

“We are the generation that is preparing,” Flores said, taking a break after a morning of classes at UNAM's architecture building. “As young people we have a different perspective, it's easier for us to contribute ideas, to help the country.”

Mendez and the many thousands of other university rejects want the same chance.

After weeks of protests this summer, including a sit-in at UNAM's main offices, Mexico's education officials have agreed to open fewer than 1,000 more slots at Mexico City's three main public universities.

“You have to struggle,” said Mendez, who hopes to get an accounting degree if he lands one of the newly-opened slots. “To get a job you need an advantage.”

This article was published in partnership with NBC News. It's part of a series — Future Shock: Millennials in Crisis — looking at how young people around the world are grappling with the transition to adulthood in a challenging global economy.