Correction: This story has been updated with the correct age for Vikiana Petit-Homme. She is 18.

NEW YORK– On a rainy Monday, students hustled into a large building in Manhattan containing two different public high schools.

Amid the hoods and umbrellas, a couple of earnest students stood near the door, waving fliers.

“You guys wanna strike today?” they asked.

As part of Teens Take Charge, the students with the fliers were carrying out a campaign they’ve honed this academic year: organizing students to walk out in protest of segregated classrooms and unequal learning conditions in New York’s public schools.

More integrated classes are possible, the student activists say, if adults in charge would take major policy steps to address the problem.

As the nation’s largest district wrestles with how to better racially and economically integrate its schools, the loudest calls for change are coming from students – young, racially diverse, digitally savvy, passionate about multiple issues, but not yet able to vote.

That’s become the norm around the world. Fed-up youth are agitating for movement on a variety of causes, from a cleaner environment and stricter gun control to more social and educational equality.

The global climate crisis has proved the most visible rallying point. Thanks in part to actions by 17-year-old Swedish activist Greta Thunberg, millions of schoolchildren participated in a worldwide strike last fall to urge corporations and lawmakers to lower carbon emissions that contribute to climate change – and an increasing number of catastrophic weather events, scientists say.

Rally recap:Global strike was likely the largest climate rally ever

Weekly student strikes for climate have continued into 2020: Thunberg led one last month from Switzerland, where she was featured at the World Economic Forum in Davos with 11 other teenage change-makers.

Part of their emerging power lies in demographics: The world has never had so many young people in it. About 1.8 billion people worldwide are between 10 and 24 years old – the largest youth population ever, according to the United Nations. And almost nine in 10 young people believe their generation has a responsibility to improve the planet, according to a recent global survey.

So far, their biggest obstacle is simply to be taken seriously.

'A lot of pushback from adults'

The oldest members of the rising Generation Z – people born starting in 1997 – are just turning 22 this year, but most are still teenagers and younger, ineligible to vote and easier to dismiss.

In Davos, U.S. Treasury Secretary Steve Mnunchin said Thunberg should get a college degree before speaking about energy policy. That same week, a panel of U.S. federal court judges dismissed a 2015 lawsuit brought by 21 young people that charged the government with violating their constitutional right to life by not passing meaningful legislation to curb climate change.

“Adults have no obligation to take action on the often emotional and heartfelt sentiments expressed by children,” wrote Brandon Griggs, 15, a social justice advocate in Jacksonville, Florida, in a recent opinion piece for Education Week.

Similarly, the New York teens are struggling to get adults to change policies that would eliminate the stratification in their school system, driven in large part by school admission policies that have the effect of sorting many students by race and class.

Class warfare:New York is in uproar over push to ax gifted programs. This school is doing it anyway

“One thing I’m learning is that there’s a lot of pushback from adults,” said Karma Selsey, 17, a senior at the New York City Lab School for Collaborative Studies, and a member of Teens Take Charge.

Selsey is one of only a few black students at Lab, a selective high school mostly attended by white and Asian students from the wealthy Chelsea neighborhood, where residents get priority for seats. New York City Museum School, which shares the building, is less selective and enrolls more Latino and black students.

A stairway divides the schools and some of the resources: Lab uses Mac laptops; Museum uses Dells, students say. Lab brings in more private grants; its parent association encourages a $750 annual contribution per student. Museum relies on more federal money for low-income students.

The divides between the two schools do not reflect the diversity of the city, Selsey said, and they add to the stereotype that black and Latino students can’t learn at high levels. That’s why she led the joint walkout from both schools on that rainy day in mid-December.

Segregation:It's getting worse in schools, GAO says

“We demand that Schools Chancellor (Richard) Carranza and Mayor (Bill) de Blasio take real action and steps toward integrating the New York City high school system,” Selsey shouted into a bullhorn, as her peers surrounded her on the sidewalk.

“We are demanding a fair education for all,” she said.

Young activists among U.S. founders

Youth activism has long been a part of American democracy. Alexander Hamilton was just 21 when he signed the Declaration of Independence in 1776; John Marshall and Aaron Burr were 20 and James Monroe was 18.

In 1951, black teens in Farmville, Virginia, walked out of class to protest the substandard conditions at their segregated high school. The effort turned into a lawsuit that became part of Brown v. Board of Education, and the Supreme Court ultimately ruled schools segregated by race were unconstitutional.

Linda Brown:9-year-old girl from Brown v. Board of Education died in 2018 at age 76

In the 1960s and ‘70s, young Americans led the fight for civil rights and women’s rights and for exiting the Vietnam War.

Teen activism captured headlines two years ago when a group of survivors of the school shooting at Marjory Stoneman Douglas High School in Parkland, Florida, turned their grief into anger and became national advocates for stricter gun laws. Articulate and poised, the students were falsely called “crisis actors” by critics even as they lobbied at their state capital and gave speeches that went viral.

Never again:Parkland teens spark a day-by-day fight over guns in America

Their activism birthed March for Our Lives, a national demonstration in Washington that attracted more than a million people in support of legislation to reduce gun violence. The event spawned sister marches, then evolved into a national organization with more than 300 chapters. It recently hired its first full-time executive director.

“I’m astounded by how much of our work is totally youth-led,” said Vikiana Petit-Homme, 18, a regional director for March For Our Lives and also a freshman at the University of Massachusetts in Boston.

National rallies:At 1 million-plus strong, March for Our Lives makes powerful statement

While much of the media attention has focused on white activists, people of color focused on the same issues have often been overlooked, historians say.

“It’s not new work,” said Jerusha Conner, an associate professor of education at Villanova University and the author of “The New Student Activists,” out Feb. 18.

“It’s been steady and slow, especially in low-income communities of color," Conner said. "People are organizing, but they often have not had the national spotlight on them.”

Before Thunberg became the most recognizable young face of environmental activists, there were people like Xiuhtezcatl Martinez, 19, a hip-hop artist of indigenous Mexican descent who began speaking about protecting the environment at age 6.

Mari Copeny, 12, a black clean-water activist from Flint, Michigan, brought former President Barack Obama – and national attention – to the water contamination crisis in her city four years ago, when she was 8.

In Davos last month, The Associated Press faced backlash when Vanessa Nakate, a climate activist from Uganda who is black, was cropped out of a photo of Thunberg and three other white female climate activists. The AP apologized and republished the photo of all five young women.

Activists in New York: Strikes, meetings and pressure on mayor

Teens Take Charge and another group, IntegrateNYC, have both formed within the past five years to fight for a more integrated school system. Student leaders say they are best suited to describe what’s happening in their classrooms and what should be done to help more of their peers succeed.

The teens are now co-organizing their most ambitious action to date: A citywide, day-long walkout of schools on May 18 aimed at building youth power and pressuring the de Blasio administration to address segregation.

Six decades after Brown v. Board:Segregated classrooms persist

De Blasio and Carranza have expressed support for integration and equity across schools, but the city's Education Department has preferred to let individual communities come up with their own plans for addressing segregation.

Critics say that without stronger actions from school and city leadership, some communities will never pursue or agree on plans to integrate.

The two student groups, which are predominantly made up of youth of color, meet regularly to work on their individual campaigns to pressure city officials.

Teens Take Charge has organized brief, weekly strikes at schools, where students trumpet their views on how to even the playing field. They want high schools to drop selective admissions screening and ensure all students have access to paid internships. A department spokeswoman said officials are reviewing recommendations on admissions policies from Teens Take Charge.

IntegrateNYC has written a definition of what school integration actually looks like: diverse enrollment, equitable resources, relationships across lines of color and class, fair discipline policies and teachers whose races reflect those of their students. The definition was adopted by the de Blasio administration.

Integrate members support dropping gifted and talented programs in elementary schools and ending selective admission screening in middle schools. They also want to change the algorithm that assigns students to high schools so that more disadvantaged students, such as those with a parent who is incarcerated, or a mother who didn’t finish formal education, receive priority for seats in higher-achieving schools.

Fair access:Why one New York school ended gifted and talented

A number of the teens in both groups are some of the only black and brown faces at their elite New York schools, which are attended by mostly white and Asian students. They scored well on tests to get in and had access to great teachers with ample resources. But they also say the experience can be isolating. And they believe more New York children of color should have the opportunities they did.

Avishek Mojumdar, 16, a member of Integrate, said he didn’t really know about equity growing up. He got into a gifted and talented program because he passed the test for it at age 4, and he then got into a selective high school.

“It’s necessary for all of us to join in the activist community,” he said. “People shouldn’t be held to the same expectations in life without access to the same resources.”

The goal: 'Youth power'

Whether it’s climate change, gun control or school integration, today’s progressive teen activists are embracing a concept that has sharply divided older adults: For some groups to get more, others may have to get less.

How does a corporation pay for carbon offsets and still increase profits for shareholders? How do you restrict access to guns without telling some people they can’t have weapons?

How do specialized schools stay special if anyone can be admitted?

If elite schools in New York suddenly were to enroll large numbers of lower-achieving students, wealthy families might leave the district, or the schools’ performance metrics might drop. That’s a big concern for some parents and politicians.

And to be sure, there are young leaders among conservative activists who are pushing for very different issues.

College Republicans are at war:Nationalist 'antics' or the future of the GOP?

But for now, youth organizers calling the loudest for change seem to be united across a number of progressive causes, said Sarah "Zaps" Zapiler, executive director of IntegrateNYC.

“Despite all these issues we’re fighting for individually,” she said, “there’s this thing we’re fighting for writ large, which is youth power.”

Education coverage at USA TODAY is made possible in part by a grant from the Bill & Melinda Gates Foundation. The Gates Foundation does not provide editorial input.