In my local area, a "man with a gun call" or a "shots fired" call is a LE code: signal zero.
Police & LE should respond ASAP. I've heard the avg LE response time to a call is approx 28min. The county deputies & police in my city have taken up to 45min to answer calls for service.
As for the semi-auto rifles & handguns, the ATF, DHS or Dept of Education should put out a training video or PSA to guide schools, colleges, teachers.
There should be a uniform, fluid response to any school event that may occur.
Local PDs, FDs, first responders, and medical centers should prepare for any homeland security or active shooter events.
A few years ago, a deranged man went into the large office bldg where he was an employee & went on a spree shooting. The office bldg had no armed security or systems(access control). The metro PD's response was sub-standard. The mayor was livid. I don't blame him. The SWAT & first responders had a full scale training drill within 2 weeks.
PTAs & parents need to stay on the school admin/district. They can stop the rumors, myths & panic.
I do all my own stunts.