Once again, they filed out of class. In a new wave of school walkouts, they raised their voices against gun violence. But this time, they were looking to turn outrage into action.

Many of the students who joined demonstrations across the country Friday turned their attention to upcoming elections as they pressed for tougher gun laws and politicians who will enact them. Scores of rallies turned into voter registration drives. Students took the stage to issue an ultimatum to their lawmakers.

"We want to show that we're not scared. We want to stop mass shootings and we want gun control," said Bin...