The best way to shield a school from a gunman is to have a metal detector. Or doors that can be remotely locked. Or Twitter-trawling bots looking for threats. Or bulletproof clipboards, whiteboards and backpacks.
So says the fast-growing group of companies that sell school safety equipment. They have strengthened their marketing to school safety officials in the wake of the shooting last month at a high school in Parkland, Fla. But even as school districts rethink their security and seek to increase their budgets, they have little guidance from government agencies or independent consumer groups on which equipment would actually protect their students.