I suppose I'm conflating school shootings with mass shootings which is what most people worry about, a la Columbine or Parkland. The figures in your link are mostly gang violence, which is a completely separate although valid issue.

We do absolutely have higher rates of targeted gang violence than other countries, which after controlling for factors like density and poverty is highly correlated to young urban male demographics that aren't as prevalent in other developed nations. There is no single policy that can solve the numerous social and systemic failures that generate this problem, but due to the nature of these vendettas they would assuredly be carried out with knives and shanks in the absence of guns.