Larry Copeland

USA TODAY

In the two years since a gunman killed 20

children and six teachers at Sandy Hook Elementary School in Newtown, Conn., there have been at least 95

school shootings in the USA, including 23

in which at least one person was killed.

That's according to two groups that will release a new report Tuesday on school shootings in Washington, D.C., and issue a call for political leaders to take action to prevent gun violence.

The two groups, Everytown for Gun Safety, which calls itself the nation's largest gun violence prevention organization, and an affiliated group, Moms Demand Action for Gun Sense in America, tracked news reports for every instance of a firearm discharged inside a school building or on school or campus grounds.

In addition to their report on nearly 100 school shootings since Sandy Hook, the groups plan to release a video depicting what they say is the new "lock down" culture in the nation's classrooms.

"Tomorrow, Everytown for Gun Safety and Moms Demand Action will join with gun violence prevention leaders in Congress and survivors of school shootings to mark two years since the Sandy Hook tragedy and to release a report and video advertisement on school shootings in America," said Everytown spokeswoman Stacey Radnor. "There, we'll call on our political leaders to take action to prevent gun violence across the country."

Representatives of the two groups will be joined at a 10 a.m. news conference at the U.S. Capitol by both of Connecticut's senators, Democrats Richard Blumenthal and Chris Murphy; by U.S. Rep. Mike Thompson, a California Democrat who chairs the U.S. House's Gun Violence Prevention Task Force, and by Pamela Wright, whose 17-year-old son, Tyrone Lawson, was shot and killed in Chicago in January 2013, after a high school basketball game.

Blumenthal said he has been participating in a campaign to honor the Newtown victims with acts of kindness.

"But the best way to honor their memory is through action against gun violence," he said. "Individual acts of kindness are a very fitting memorial. But the most effective memorial is to make our nation safer and better by making our laws more effective to prevent gun violence and keep guns out of the hands of dangerous people."

He said that gun violence in the USA has claimed more than 30,000 lives since the Sandy Hook massacre. "Throughout this week, we're going to be talking about the hole in our hearts that remains and the need to fill that gaping hole in our hearts by continuing to fight for common sense, sensible (laws) that keep faith with those 26 wonderful children and educators and the more than 30,000 victims who have perished from gun violence since the Dec. 14th massacre."

According to their website, Everytown for Gun Safety was born this year out of the merger between Mayors Against Illegal Guns, founded in 2006 by then-New York City Mayor Michael Bloomberg and 14 other mayors, and Moms Demand Action for Gun Sense in America, which was begun by stay-at-home mom Shannon Watts of Indianapolis in response to the Sandy Hook school shooting.

On Dec. 14, 2012, Adam Lanza, 20, shot and killed his mother then drove to Sandy Hook Elementary School and launched the nation's deadliest mass shooting at a high school or grade school. He then shot and killed himself.