When making a decision as to whether something is small, large, or tiny one needs a scale. What's the scale here? For example, if the rest of the world combined has had 12 mass k-12 shootings, then American accounts for 40% of the total shootings which is a huge fraction. So in my original question I was trying to find the right scale.
Edit: In a comment below, this article was linked https://qz.com/37015/how-school-killings-in-the-us-stack-up-.... Indeed, on this scale we see a very different picture!