There were so many questions after 17-year-old Ely Serna brought a shotgun to his Ohio school and opened fire in 2017, wounding two.

Along with the whys, West Liberty-Salem High School assistant principal Andy McGill recalled thinking, "Is there something I missed?"

"I never would have thought in a million years that it would be that person," he said.

The questions now focus on how to prevent anything like that from happening again. Schools like McGill's have been setting up teams to assess threats posed by students who display signs of violence, like another Ohio student, Connor Betts, who co...