Kids are maturing later and getting the same access to things they aren't mature enough to handle not to mention those things are more deadly than ever.
You act as if school shootings happen all the time and has been going on forever. I looked it up and here is the stats up to Feb 2018.
List of school shootings as of February 2018
2018, 14 February - Marjory Stoneman Douglas High school shootings - (17 dead)
2017, November 14 - Rancho Tehama Reserve shootings - (6 dead)
2015, 1 October - Umpqua Community College shooting - (10 dead)
2014, October 24- Marysville Pilchuck High School shooting - (5 dead)
2013, June 7 - 2013 Santa Monica shooting - (6 dead)
2012, December 14- Sandy Hook Elementary School shootings - (28 deaths)
2012, 2 April - Oikos University shooting - (7 deaths)
2008, February 14 - Northern Illinois University shooting - (6 deaths)
2007, 6 April - Virginia Tech massacre - (33 deaths)
2006, October 2 - West Nickel Mines School shooting - (6 deaths)
2005, 21 March - Red Lake shootings - (10 deaths)
1999, 20 April - Columbine High School massacre - (15 deaths)
1998, May 21 - Thurston High School shooting - (4 deaths)
1998, March 24 - Mitchell Johnson and Andrew Golden - (5 deaths)
1991, 1 November - University of Iowa shooting - (6 deaths)
1976, 12 July - Fulerton, California - (7 deaths)
1970, 4 May - Kent State shootings (4 deaths)
1966, 12 November - Mesa, Arizona - (5 deaths)
1966, 1 August - University of Texas tower shooting - (17 deaths)
1940, May 6 - Pasadena - (5 deaths)
1893, December 13 - Charleston - (6 deaths)
1893, March 26 - Plain Dealing high school - (4 deaths)
1764, July 26 - Enoch Brown (10 deaths)
The one at Kent State was the National Guard who did the shooting. You had a total of 8 school shootings from 1764 through 1990. After 1990 till Feb 2018 there was 15 plus however many happened after that. In 226 years we had 8 and in 28 years we had 15 plus however many happened after that date.
School shootings weren't common prior to 1990. After 1990 they have become so. There's something that happened to these kids or didn't happen to these kids that should have.