(CNN) For the second time in two months, thousands of students from across the country streamed out of class as part of a National School Walkout to demand action on gun reform -- even as Florida police investigated a fresh shooting that injured a student Friday morning.

Students walked out of class at 10 a.m. Friday in each time zone to observe a moment of silence for shooting victims; many are then moving on to other actions, such as rallies in the larger cities or volunteer work.

Before Friday's walkouts began, the latest school shooting happened in Ocala, Florida, northwest of Orlando. Police said a student was shot in the ankle at Ocala's Forest High School , and a suspect is in custody.

Friday's walkouts, while drawing momentum from February's mass shooting at South Florida's Marjory Stoneman Douglas High School , also marks the 1999 Columbine High School massacre in Colorado in which two gunmen killed 12 students and a teacher.

Student activists rally against gun violence at Washington Square Park in New York.

Student activists rally against gun violence at Washington Square Park in New York.

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

Students from the Nashville, Tennessee, area gather at Public Square Park to call for gun law reform.

Students from the Nashville, Tennessee, area gather at Public Square Park to call for gun law reform.

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

Student activists participate in a "die-in" to protest gun violence at Washington Square Park in New York.

Student activists participate in a "die-in" to protest gun violence at Washington Square Park in New York.

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

Students at Clayton-Bradley STEM Academy in Maryville, Tennessee, set up chairs representing every US school shooting since 2000.

Students at Clayton-Bradley STEM Academy in Maryville, Tennessee, set up chairs representing every US school shooting since 2000.

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

Ryan Deitsch, right, a high school senior, carries a sign that reads "love" as he joins his fellow students from Marjory Stoneman Douglas High School, where 17 classmates and teachers were killed during a mass shooting in February, for the National School Walkout in Parkland, Florida.

Ryan Deitsch, right, a high school senior, carries a sign that reads "love" as he joins his fellow students from Marjory Stoneman Douglas High School, where 17 classmates and teachers were killed during a mass shooting in February, for the National School Walkout in Parkland, Florida.

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

Several hundred high school students from the Washington area observe 19 minutes of silence while rallying in front of the White House before marching to the US Capitol.

Several hundred high school students from the Washington area observe 19 minutes of silence while rallying in front of the White House before marching to the US Capitol.

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

Several hundred high school students march from the White House to the US Capitol to rally against the National Rifle Association (NRA) and call for stricter gun laws in Washington.

Several hundred high school students march from the White House to the US Capitol to rally against the National Rifle Association (NRA) and call for stricter gun laws in Washington.

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

Students at Naples High School, in an effort to revive action on gun reform, walk out of school in Naples, Florida.

Students at Naples High School, in an effort to revive action on gun reform, walk out of school in Naples, Florida.

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

Eugena King, senior class president at Herron High School, speaks out to fellow students at the Soldiers and Sailors Monument in Indianapolis.

Eugena King, senior class president at Herron High School, speaks out to fellow students at the Soldiers and Sailors Monument in Indianapolis.

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

Hundreds of students gather on the steps at the State Capitol in St. Paul, Minnesota.

Hundreds of students gather on the steps at the State Capitol in St. Paul, Minnesota.

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

Students embrace as others raise their fists in a moment of silence for victims in Los Angeles.

Students embrace as others raise their fists in a moment of silence for victims in Los Angeles.

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

A student holds up her hands while taking part in National School Walkout Day to protest school violence Friday, April 20, in Chicago. Students from around the nation joined in the walkout against gun violence on the 19th anniversary of the shooting at Columbine High School.

A student holds up her hands while taking part in National School Walkout Day to protest school violence Friday, April 20, in Chicago. Students from around the nation joined in the walkout against gun violence on the 19th anniversary of the shooting at Columbine High School.

US students rally against gun violence in second walkout

Photos: US students rally against gun violence in second walkout

Many students across the country say not enough has been done to help prevent mass shootings. In Florida, Stoneman Douglas freshman Ryan Servaites pointed to Friday's shooting in Ocala.

"The fact that it happened on this day, in a way, reinforces what we are trying to get across," he said.

"Enough is enough. Children are dying. Children are being hurt. We won't stop. This is why."

Besides observing moments of silence, other actions during the day have included marching to a local lawmaker's office, allowing open-mic time for students to share concerns and helping register those who are eligible to vote. Students at more than 2,500 schools were to participate.

Hiam Baidas joins demonstrators in Lafayette Square in Washington.

In Washington's Lafayette Square across from the White House, high school students gathered well before 10 a.m.

One of those demonstrators, Hiam Baidas of Falls Church, Virginia, said the country needs laws making it more difficult to buy guns.

"Right now I'm 18 years old, I live right across the street from Walmart, and I can go buy a gun -- and I don't think that's OK," she said.

"I think the youth are the movement that is going to change and better our country."

Washington area students observe moments of silence Friday while rallying in front of the White House.

In New York's Washington Square Park, demonstrator Arielle Geismar, 16, said students will be persistent until gun laws are tightened.

"I've grown up in the generation of students who are realizing that we have lockdown drills all the time. We live with the constant fear that there is the possibility of a school shooting. No one should have to live like that," said Geismar, co-founder of the gun control activist group NYC Says Enough.

Hundreds of high school students gathered in Chicago's Grant Park to hear speeches.

"The Second Amendment has been used to undermine my First Amendment rights to speak and live long in happiness!" Brendan Smith, a sophomore at Chicago's Kenwood Academy, told the crowd.

Brendan Smith, a sophomore at Kenwood Academy, addresses a crowd Friday at Chicago's Grant Park.

Current students at Columbine did not walk out, because classes are canceled annually on the anniversary of the 1999 shooting. The students are encouraged to take part in community service.

On Thursday, Columbine survivors, as well as some current Columbine and Parkland students, met Thursday in a park in Littleton, Colorado , to remember those lost.

Facing unexcused absences

In contrast to the March 14 national walkout -- in which students generally walked out for 17 minutes, one minute for each person killed at Stoneman Douglas -- many planned to walk out for the rest of Friday's classes.

So they may not see the same kind of leniency from school officials that some saw last month.

At Stoneman Douglas in Parkland, where a gunman massacred 17 people two months ago , Principal Ty Thompson told students Thursday that they will face disciplinary action if they leave campus.

The work we have done today is beyond anything I thought I would ever see. There is so much more to come. I love you all! #NationalSchoolWalkout pic.twitter.com/cRxfaR30DG — Lane Murdock (@lanemurdock2002) April 20, 2018

Several teachers told CNN that the disciplinary action will be an unexcused absence

Students in New York City who walk out for remainder of the day also will be marked with unexcused absences, city public schools spokeswoman Miranda Barbot said.

On Friday morning, Stoneman Douglas students held moments of silence in a courtyard and then made a choice -- some remained on campus, but others left for a community park, where they volunteered to pick up trash. Student leaders urged both groups to register to vote.

Activist David Hogg, left, and other Parkland students join in the national walkout Friday.

Among those who walked out was student and gun control activist David Hogg

"We're a diverse but unified front," Hogg said. "We have different ideas of how to go about this, and I think that's great, because we can do multiple things."

"So long as you register to vote, and so long as you vote on these issues in November, that's all that matters here," he said.

Some students are walking out of their classrooms today to protest gun violence on the anniversary of the Columbine shooting. Others want to make it a day of service. Watch CNN's Dianne Gallagher explain more. https://t.co/zhP4SnLeT2 — Meg Wagner (@megwagner) April 20, 2018

Stoneman Douglas teachers got an early start Friday, demonstrating outside the building before classes began.

Those teachers combined calls against gun violence with requests for more school funding.

"Enough is enough!" they chanted, holding signs with messages such as "Children's lives > assault rifles," "Arm me with school funding" and "Arm me with better pay and lower class size."

Teachers at Florida's Marjory Stoneman Douglas High School demonstrate before classes Friday.

The organizer

She was disturbed by her own reaction -- or lack thereof -- to the February massacre in Florida.

"When I found out about the shooting at MSD, I remember I didn't have a huge reaction. And because of that, I knew I needed to change myself, and we needed to change this country," Lane said.

"We should be horrified, and we're not anymore. It's American culture."

Lane said students should be empowered "to do the walkouts and become leaders in their communities, speaking up when they see inaction."

Lane's father, Paul Murdock, said Friday's shooting in Ocala was infuriating.

"No more words from the NRA and politicians. These kids will vote them out," he said.

Friday's walkout is among a series of nationwide events calling attention to gun violence. Besides the March 14 walkout, thousands of students, teachers and supporters held March of Our Lives rallies on March 24, a Saturday, in cities around the world.

Push for legislation

The movement encourages young people to push for legislation at the state level if Congress doesn't act.

"The federal government can set standards and practices that apply to all states around gun safety. But states have the option of passing additional measures to protect their own residents from gun violence," its website says.

JUST WATCHED David Hogg: The people in power are shaking Replay More Videos ... MUST WATCH David Hogg: The people in power are shaking 01:36

Students are calling for several measures, including banning assault weapons, high-capacity magazines and bump stocks; mandating universal background checks; placing a minimum age of 21 on all gun purchases; implementing waiting periods between a gun purchase and gun transfers; and allowing families to petition a court to remove guns from individuals at risk of injuring themselves.

While there hasn't been major congressional action since the Parkland massacre, some cities and states have toughened gun control.

In Florida, after Parkland students rallied at the state Capitol , Republican Gov. Rick Scott signed a gun bill called the Marjory Stoneman Douglas High School Public Safety Act . It raises the minimum age to buy any firearm in the state to 21, bans the sale or possession of bump fire stocks and adds $69 million in funding for mental health services in schools.

In Vermont, Republican Gov. Phil Scott banned bump stocks , limited the size of magazines, expanded background checks for gun purchases and raised the minimum age to purchase firearms to 21.

CORRECTION: This story has been updated to describe the number of shooters in the Columbine massacre.