Since the shooting on Valentine’s Day, when 14 students and three staff members were killed, a group of surviving students and parents of the victims have led a vocal gun-control movement that has spread the country.

With the November midterm elections in mind, survivors of the shooting said Monday that they would take their gun-control and voter-registration message on a two-month bus tour of the country this summer, seeking to raise awareness of the preponderance of school shootings, the easy availability of weapons, and the financial ties of many politicians to the National Rifle Association.

“We are trying to get the most people to vote,” said Emma González, who graduated from the school on Sunday and is one of the movement’s most prominent leaders. She and others, holding placards with the legend “Road to Change,” said they planned to visit about 75 communities around the nation, as well as every congressional district in Florida.

The activists’ biggest effort so far was the March for Our Lives, a series of demonstrations on March 24 around the country and overseas. More recently, Stoneman Douglas students protested the Publix supermarket chain’s support of a Republican candidate for governor, Adam Putnam, a strong proponent of the N.R.A. On May 25, faced with students staging a “die-in” by lying on the floor of a Publix supermarket in Coral Springs, the chain said it would immediately suspend all contributions to political campaigns.

After spending much of the last three months under a media glare, the Stoneman Douglas seniors tried to keep Sunday’s graduation ceremony to themselves, with reporters barred from attending.