"Gun free zones" are a joke. They'd be better labelled as "10 minutes of free-fire before someone with guns who can stop you shows up zones".
In the world we live in (in the US), most or all schools are effectively "gun free zones". So we can discuss that side of the argument with plenty of facts and statistics. Your hypothetical armed school zones are really only a thought exercise at the moment. Why don't you get together with other gun rights folks that feel the same way and start an experimental community with all of your kids (you do have kids in public school, right?) going to a school loaded with guns (no pun intended). As long as you have a fairly representative sampling of people (no cherry-picking only truly "responsible" gun owners, good representation from all socioeconomic groups), it would be an informative experiment, even with a sample size of only one school. And after a decade or so of no gun violence on campus, you can remind us all of how right you were.
Until then, I'll stick with the statistics that show that my kids are slightly more likely to die due to a dog attack than from a school shooting.