School shootings

NPR -  There have been more than 400 school shootings since Columbine in 1999, according to an analysis by The Washington Post. The latest was last month, when a former student opened fire at a Catholic school in Minneapolis. Two students were killed and at least 18 other people were wounded.

In the wake of those shootings, an industry has emerged to try to protect schools — and business is booming. According to the market research firm Omdia, the school security industry is now worth as much as $4 billion, and it's projected to keep growing.

"The school safety and security industry has grown rapidly over the past decade," says Sonali Rajan, senior director with the research arm of Everytown for Gun Safety, which advocates for gun control. "The challenge right now is that these school safety products, the vast majority, have absolutely no evidence guiding their effectiveness."