I'd argue that it's not so much a case of "it works" ("it" meaning the armed volunteers in schools) as it is a case of a number of things working together that work in the country implementing them. Australia's response to the Monash University shooting was arguably the exact opposite of the Israeli solution, and it's worked well for them, too.
I don't think school shootings can be solved with just one simple solution. I wish I could believe that; one of my younger sisters is an elementary school teacher, and she teaches at the same school her children currently attend. I don't want to wake up one morning and hear that she took a bullet for her kids. I don't even want to hear that she led her kids to safety. I want the most exciting news story for her school to be about a new library or new classroom equipment.
I think we'd be better off starting out by looking at the precursor behaviors of those who commit mass murder. "Precursor behaviors" is a phrase I'm choosing very deliberately, and NOT as a synonym for "diagnostic label." Diagnostic labels aren't always applied accurately, or in time to be useful. If we can determine the X plus Y (and however many other letters) that lead to the Z of someone becoming a mass murderer, looking at the actual facts of the past cases, then I think we'd be more likely to come up with a solution that works in this country. Unfortunately, this requires a lot of people to put their own biases and agendas aside, and we don't have a good recent history of exercising that sort of objectivity and teamwork.