im betting about 90% of all "threats" that schools deal with are completely empty threats.
my school has had several bomb threats in the past and all of them actually turned out to be pranks
and most of the time, schools that actually do suffer mass-shootings and bomb explosions never had any prior warning of it. people who want to carry it out are 99% of the time smart enough not to tell anyone.
school districts and police departments are wasting time and money overreacting to jokes by people who just want to get a ruse out of everyone