"I was going to give a speech about Meadow and how devastated I am and how we need to make change, but they won't allow me to put my voice out", said Hunter Pollack, whose sister, Meadow, was one of 17 people killed in the shooting at Marjory Stoneman Douglas High School on February 14. She wore an orange anti-gun violence ribbon and a blue and black March for Our Lives symbols.
Protestors and rally-goers, not quite sure what was happening, started to chant, "Never again!"
Underlining sharp differences among the American public over the issue, counter-demonstrators and supporters of gun rights were also in evidence in many US cities.
"Emma stood for 6 mins and 20 seconds to honor the lives of 17 gone too soon". They are calling for common sense gun policies, like universal background checks and raising the age limit to buy an assault rifle.
"Gun-hating billionaires and Hollywood elites are manipulating and exploiting children as part of their plan to DESTROY the Second Amendment and strip us of our right to defend ourselves and our loved ones", the NRA said in the post. Gonzalez's father migrated from Cuba to the United States.
It's one of several posts on King's page that have been critical of the activism displayed by the Parkland shooting survivors advocating for gun control.
She talked about her friend Carmen: a victim killed in the shooting, who would no longer complain about piano practice to her.
Watch her full emotional speech below. For most of the time that she addressed the crowd, Emma went silent, giving us one of the most powerful moments of the day.
White House deputy press secretary Lindsay Walters said the administration applauded "the many courageous young Americans" who exercised their free-speech rights.
"It's pretty simple for me", said Zoe Tate, 11, from Gaithersburg Middle School in Maryland, explaining why she marched in Washington. The movement even spread globally, with people marching in Canada, Iceland, Spain, Israel, India, Hong Kong, and more worldwide locales. "Let's keep the guns out of the hands of the wrong people and keep them in the hands of the safe and reasonable", she said.