Two years ago, California passed a restriction concerning concealed carry on school campuses. Now, permit holders can only carry a handgun with school administration approval. Out of the 977 school districts in California, only five decided to allow concealed carry on their campuses. But the state Assembly is about to vote on a bill that would prohibit carrying in even these five school districts.

There seems to be a particular fear of allowing concealed handguns on school property. Assemblyman Kevin McCarty, D-Sacramento, is sponsoring Assembly Bill 424 to take away local control over concealed carry on school grounds. He argues: “A safe learning environment is … not possible if a school district allows armed civilians to roam California school campuses.”

But the simple fact is that there haven’t been any problems. Prior to the early 1990s, there were no state laws specifically restricting concealed carry on K-12 property. In 2015, when California became the first state in at least 40 years to pass a law restricting concealed carry on school grounds, no one could point to a single incident in California. That hasn’t changed in the last two years.

A common fear is that someone will take away a teacher’s gun and misuse it. But this has never happened. Excluding off-hours firearms training on school grounds, there has only been one accidental discharge involving a permit holder on K-12 property. This happened in Utah in 2014, and resulted in only a very minor injury.

“From what I’ve seen in Utah, [school insurance] rates have not gone up because of guns being allowed,” says Curt Oda, former president of the Utah Association of Independent Insurance Agents. Surveys in other states have also found no evidence of increased insurance costs.

Twenty-five states now allow teachers and staff to carry, though the rules vary. Utah, along with Alabama, New Hampshire and parts of Oregon, allows teachers and staff to carry at their own discretion. Other states require the approval of the superintendent or school board. In Ohio, at least 40 school districts allow teachers to carry.

Others are concerned that permit holders will accidentally shoot bystanders, or be mistaken for the attackers by the police when they arrive.

Permit holders have stopped dozens of would-be mass public shootings in malls, churches, schools, universities and town centers. In none of these cases has a permit holder ever shot a bystander. Nor have police ever accidentally shot a permit holder.

Despite the fears of permit holders not being justified, California already requires substantially more training than in most of these other states.

Unfortunately, gun-free zones, such as what McCarty wants, don’t make places “safe.” Since at least 1950, all but four mass public shootings in America have taken place where citizens are banned from carrying guns.

Unsurprisingly, killers try to avoid armed resistance. Last year, a young Islamic State sympathizer planned to shoot up one of the largest churches in Detroit. In a wiretap, the FBI recorded the young man’s explanation for why he picked the church: “It’s easy, and a lot of people go there. Plus, people are not allowed to carry guns in church. Plus, it would make the news.”

These killers might be crazy, but they aren’t stupid. They want to kill as many people as possible, and that means picking defenseless targets where no one will have a gun.

The term “gun-free zone” is what should really make people nervous. They are magnets for murderers. Even the most ardent gun-control advocates never put “Gun-Free Zone” signs in front of their homes. Let’s stop putting them elsewhere.

John R. Lott, Jr. is the president of the Crime Prevention Research Center and the author most recently of “The War on Guns” (Regnery, 2016).