Since I was a teenager, I’ve shot many kinds of guns: handguns, shotguns, rifles—and an AR-15. They each have different characteristics, but they’re all capable of piercing a typical high school wall or window. If teachers are armed, all of those teachers must be able to instantly think like Joe Zamudio: Will my bullet hit the right target? Is that person who is waving a gun around the shooter, or could it be the person who just pulled the gun out of the shooter’s hand (like in Tucson)? What if I miss? Where does the bullet stop? How many of those skinny walls and windows will the bullet pierce before it drops? If I’m firing a high-powered gun, will the bullet pass through the shooter and hit another student? And will the police think I’m the shooter if they see me with a gun?

These are not hypotheticals. These are real considerations trained police officers face when dealing with active shooters. But teachers aren’t cops. Even with the cursory gun training some politicians have suggested, teachers would lack the real-world experience of a full-time officer. Police also keep their guns secured—another aspect of their training. If, let’s say, a million teachers have guns, how many will be left unsecured by irresponsible teachers? If it’s even 1 percent, that means 10,000 handguns could be near the reach of children every day.