It's been 15 years since the shooting at Columbine High School brought gun control issues to the forefront. From Virginia Tech to Newtown, here's a look at how gun control groups have tried to sway the debate through their ads. (Julie Percha/The Washington Post)

April 20, 2014, marked 15 years since two students armed with guns entered Columbine High School in Littleton, Colo., and killed 13 people in one of the deadliest school shootings in U.S. history.

Since Columbine, the nation has been shocked by shooting massacres at Virginia Tech, Sandy Hook Elementary and many other communities, but little has changed when it comes to legislation. The news involving gun violence has left prominent gun control groups searching for a message that will spur change in the nation’s firearm laws.

The latest ad campaign by Everytown for Gun Safety focuses on the need for families to lock up guns in the home and features a tense scenario where two young children stumble upon an improperly stored firearms.

From cringe-worthy television spots to heart wrenching testimonials, here are some of the ways gun control groups have tried to reach voters and policy makers.