Marjory Stoneman Douglas High students mourning the deaths of 17 peers in a shooting rampage have a message to lawmakers: Never again.

"It's time for us to stand up and take action and hold our elected officials responsible," said David Hogg, a senior who shot cell phone video from inside the school as he hid in the dark from the shooter, who stalked the hallways of the Parkland, Florida school on Valentine's Day.

Later this week, a group is heading to Tallahassee to speak with state legislators. In addition, a CNN town hall meeting with Parkland teens is scheduled Wednesday with lawmakers; Florida Sens. Marco Rubio and Bill Nelson are among those who have accepted invitations, but Gov. Rick Scott on Monday declined an invite to attend.

The main message: Address gun reform now.

"This isn't about the GOP. This isn't about the Democrats. This is about us creating a badge of shame for any politicians who are accepting money from the NRA and using us a collateral," Douglas junior Cameron Kasky said.

"We're going to be facing this with trepidation and determination and we have an incredible support system around us and we are going to be the difference," senior Emma Gonzalez said.

This movement already has events set for next month. On March 14, Women's March organizers are planning a 17-minute nationwide school walkout to protest gun violence. Ten days later, a march on Washington is scheduled, where students -- many not old enough to vote — will push for stronger gun legislation.

"You're either with us or against us. We are losing our lives while the adults are playing around," Kasky said.

"To every politician who is taking donations from the NRA: shame on you," Gonzalez added.

Chris Grady, a 19-year-old senior at the Parkland school, was one of several students at a rally Sunday near the campus.

"The kids in Newtown were too young to understand what happened and were too young to have their own voice," Grady said, referring to the 20 first-graders killed in the 2012 Connecticut school shooting. "We want to be the voice for those kids and thousands of others."

Information from the Associated Press was used in this report.