From Washington to Los Angeles, students walked out of US classrooms Wednesday in the largest grassroots protest against gun violence seen in years as the House of Representatives approved spending more money on school security measures. Hundreds of teenagers from Washington area schools gathered outside the White House, holding up signs reading "Books Not Bullets" and "Protect People Not Guns" before marching on the US Capitol. "We want to show Congress and politicians we are not standing by, we are not silent anymore," said 17-year-old Brenna Levitan, who was at the protest with her mother.  Students in dozens of other cities in all 50 states staged similar demonstrations and observed a moment of silence to honor the 14 students and three adult staff killed a month ago at Marjory Stoneman Douglas High School in Parkland, Florida. In Los Angeles and other cities, teenagers spelled out the protest slogan "#ENOUGH" by lying down on the ground on sports fields. In Washington, several hours after the protests broke up, US lawmakers took their first significant step to address school gun violence since the Parkland shooting. The House of Representatives voted 407-10 to fund violence prevention measures at schools including boosting security, mental health screening and creating anonymous reporting systems so students can report threats. But Congress has yet to tackle the more controversial aspects of gun control demanded in the wake of the Parkland shooting. These include expanded background checks for gun sales, a ban on assault weapons and raising the minimum age for some firearms purchases. The United States sees more than 30,000 gun-related deaths annually and Stoneman Douglas students have spearheaded a national gun control campaign, helping to force through a new law on age limits for gun purchasers in Florida. The US public supports tougher gun laws, according to polls, but there is little backing for meaningful reforms in the Congress. According to the #ENOUGH" campaign, students from more than 3,000 schools nationwide took part in Wednesdays demonstrations.