Re: The media strikes again!
"There's been more in the last decade than in all of US history before 1990 though."
And you can prove this how? You might well be right, but how would you determine it with any confidence? In fact, has the dwell time of children in school increased? If so, has that had an affect on the number of shootings? Prior to WWII there was considerably less demand for "children" to remain in school and get a diploma. A trade that could support a person or a family was more encouraged.
Consider serial killers as another example of truly egregious behavior and our perceptions of them. Modern fiction and media would have you think they are springing up more commonly now than ever before. Yet looking back in history, there were Gilles de Rais, Countess Bathory both remarkably monstrous. No media per se though so no "media" accounts. Burk and Hare, serial killers for profit: limited media. Jack the Ripper (not just a serial killer but also a cannibal) who likely moved to the US and continued his career for years: lots of English media, but it takes serious work to comb through various disparate and geographically remote city news papers to discover that Jack may be been active for a long time after he disappeared in from England. Albert Fish, another cannibal, but US media is coming into its own. Then, the depression and WWII eclipses a good deal of what would otherwise be front page news. The FBI is only starting to keep statistics, Korea, Viet Nam, and Zodiac. All we can be sure of is that the media itself has become remarkably proficient at reporting things and that increased efficiency correlates very well with increased public perception of risks.
It maybe that there really are more shootings. It may be that the media inspires more shootings, or it may be that the incidence is a function of population growth and increased media efficiency combine to create a perception of changes that are illusory.