School and other mass shootings have unfortunately become a regular part of American life.
Via Reddit, this chart, from Noel Bautista of ArmchairScholar.com shows the number of school shootings in each year from 1990 to 2014, not including today's shooting at Reynolds High School outside Portland. There's been a stark increase in the last few years:
As a big caveat, the chart was made using data from Wikipedia's list of school shootings in the U.S., and so it's possible that older shootings could be under-reported in the data. Regardless, the number of shootings in recent years has been enormous, and a comparison with other studies shows that they are in fact on the rise.
For other charts illustrating deaths and injuries from shootings, and the geographic breakdown of shootings, check out the original post on Armchair Scholar.