There were mass shootings in the 60s and yet the media reaction was different.
The first “Official” mass murder was in 1949 New Jersey.
https://www.smithsonianmag.com/history/story-first-mass-murder-us-history-180956927/
However, if you really study the past you will find mass killings and serial killers going back to the 1700s, including the first school house massacre in 1764 Pennsylvania.
http://pabook2.libraries.psu.edu/palitmap/Enoch.html
And in Canada to the north...
https://www.cbc.ca/news/canada/deadly-shootings-schools-canada-1.3416685