Earlier quoted context omitted.
Also, how come the incidence of these types of shootings are so much lower in other parts of the world if there is no policy that will help prevent them?
Law is not the only variable and is not deterministic. Social environment and cultural values are of great influence. The US media glorifies violence and yet censors the reality of it. How many of those other countries with stricter gun control laws have been involved in as many violent conflicts across the globe as the US?
(also, perhaps surprisingly to Americans, school trained me on guns at 14: http://atc.wikia.com/wiki/L98A2_Cadet_GP_Rifle )