Leaving it up to local communities to decide is much better than trying to create a one size fits all solution. I grew up in the city, and from my high school you could get up on a building and hit a golf ball to the nearest police department. Did my high school need an armed guard? Probably not. On the other hand my fiance grew up in a town near the mexican border with one 400 kid high school in a district of almost 400 square miles, and an average police response time of over 10 minutes. An armed guard or at least some armed teachers would definately make an impact in the event the worst happens there.