US students have spilled out of classrooms by the thousands, waving signs and chanting slogans like "We want change" in a coast-to-coast protest against gun violence prompted by a deadly rampage at a Florida high school last month.
The hashtag ENOUGH National School Walkout began in the Eastern time zone at 10am on Wednesday and was scheduled to last 17 minutes, though many protests went longer.
The protest rolled westward, with students in other time zones walking out at 10am local time, including at Colorado's Columbine High School, where two gunmen killed 13 people in 1999.
The announced duration of the walkouts was intended to commemorate the 17 students and staff killed at Marjory Stoneman Douglas High School in Parkland, Florida, on February 14. The massacre was the latest in a series of shootings that have plagued US schools and colleges since the Columbine attack.
Many school districts gave their blessings for the protests, but others warned of discipline for any students who joined the walkout, though many defied the warnings and left school anyway.
In Parkland, thousands of students slowly filed on to the Stoneman Douglas school football field to the applause of families and supporters beyond the fences as law enforcement officers looked on. News helicopters thrummed overhead.
"We want change!" students chanted on the footpaths outside the school. "Can you hear the children screaming?" read one of the signs.
At New York City's Fiorello H. LaGuardia High School, crowds of students poured into the streets of Manhattan, many dressed in orange, the colour adopted in recent years by the gun-control movement.
"Thoughts and prayers are not enough," read one sign, needling the rote response many lawmakers make after mass shootings. At 10am, the hundreds of students sat down on the footpath, filling half a city block, and fell silent.
"We don't feel safe in schools anymore," said Sarah Chatfield, a high school student from Maryland, standing in a crowd of hundreds protesting outside the White House, with some sitting silent with their backs turned.
"Trump is talking about arming teachers with guns," the 15-year-old said. "That is not a step in the right direction."
Some of the students began marching toward Capitol Hill. "Hey hey, ho ho, the NRA has got to go!" they chanted, referring to the powerful gun-rights interest group, the National Rifle Association.
The NRA sent out a defiant tweet on Wednesday morning that included a picture of an assault-style rifle and a comment saying: "I'll control my own guns, thank you."
In districts where school authorities warned against joining the protests, some students protested anyway.
About 200 students walked out of the Council Rock High School North building in Newtown, Pennsylvania, despite warnings from school administration that doing so would bring discipline.
"Students deserve the right to go to school feeling safe and comfortable, not feeling scared that their school will be the next target," a student said into a megaphone to the group outside.
Australian Associated Press