Since Columbine introduced the modern school shooter in 1999 there have been over 30 mass casualty school shootings in the United States alone.Innocent lives lost because there were no deterrent in place to deter an active shooting situation.
In just 2 years from 2013 to 2015 there were 59 deaths. In 2018 there have already been multiple shootings and over 20 dead in less than 2 months.
The CDC in 2016 found over 90% of all schools had a written plan for responding to a school shooting.
They further state that 70% had drilled with the students to prepare for an event.
What they do not have is an armed deterrent in most cases. When there was an armed deterrent in almost all cases the shooter was stopped before they could kill more students.