A sign hangs on a fence at Marjory Stoneman Douglas High School in Parkland, Florida on February 27, 2018. Rhona Wise | AFP | Getty Images

This time, the debate is different. The Feb. 14 school shooting at Marjory Stoneman Douglas High School in Parkland, Florida, which left 17 dead, has sparked youth activism for gun reform. Mass shootings typically are followed by outrage, cries for gun reform, heavy media coverage —and reactionary anger from pro-gun activists — before fading. This time, however, teenagers are leading the charge armed with a tool they have embraced most of their adolescent lives: social media. The #NeverAgain hashtag, founded by students and survivors of the incident, is demanding restrictions on guns as a way to end mass murder in schools.

'They know how the media can coordinate'

A 2007 mass shooting at Virginia Tech left 32 dead, and the 2012 massacre at Sandy Hook Elementary School killed 27 — including 20 children between 6 to 7 years old — but neither of those mass murders brought about substantive national change. But the level of personal information-sharing, reaction and attention are higher today, because of social media.

The students in Parkland and others are proving good at galvanizing segments of the public, asking good questions, and shaming adults who continue to support the National Rifle Association, according to Kristin Goss, an associate professor of public policy at Duke University. "In the case of Virginia Tech, college kids got involved in gun reform movements after the shooting. But they were not using social media on a scale like Parkland," Goss said. "They were off the radar." Emma Gonzalez, a survivor of the shooting who joined Twitter three weeks ago, has amassed a following of 1.19 million. The NRA, which has been on the social media app since 2009, has 614,000 followers.

Social media is central to students' lives

Social media is a central part of daily life for the Parkland students and their age group generally, said Darrell Miller, a professor of law at Duke University. "One difference between this shooting and the other tragedies is that the survivors today are kids who have grown up in a world saturated with media and the internet," Miller told CNBC, adding that "they know how the media can coordinate like-minded individuals to make things happen."

Demonstrators hold signs during a 'lie-in' demonstration supporting gun control reform near the White House on February 19, 2018. Zach Gibson | Getty Images

"Historically, gun control movements have faced shortage of money and had trouble mobilizing citizens at a grassroots level," Goss said. "The movement has also struggled to find a compelling message to counter that of the NRA, which is patriotic — associating firearms with American values of democracy and freedom," she said.

Companies act on their own

It's far from certain that the #NeverAgain hashtag will bring about any change out of Washington, which is controlled at all levels by Republicans who are the NRA's strongest political allies. Commercial interests are a different story. Walmart, which had already banned sales of assault rifles in its stores since 2015, raised the age limit for gun purchases in stores to 21, while Dicks Sporting Goods moved to ban sales of assault rifles in its stores. "It's significant, the steps that Walmart and Dicks have taken, with assault rifles being some of the most — if not the most popular guns in the U.S. right now," Ruben said. Major retailers Kroger and L.L. Bean raised the age limit for gun purchases in stores to 21 last week, while outdoor goods merchant REI moved to stop purchases from Vista Outdoor until that company provides a public statement to outline its strategies after the shooting.

Adults get on board