This is a perfect example of why we need more than just one or a handful of armed officers in a school. There is no reason why LTC holders (or the equivalent in other states) should be forced to disarm when entering a school. We have allowed legally armed citizens around children for many years now without major incident. There is simply no negative to this, and when there is no negative and only positive to a choice, that choice becomes obvious.
Teachers who are uncomfortable carrying a gun should not be forced to carry a gun. That addresses the complaint of the teachers union and the "resist everything" lawmakers in congress.
Everyone else who is licensed to carry a gun should be able to do so. Just repeal the GFSZA and any state prohibitions on carry in schools. As government owned / operated buildings, they would actually be prohibited from posting 30.06 in Texas.
Supplement the willingly armed teachers and parents who happen to be present naturally with a dedicated security force comprised of some LEO's along with a trained volunteer force made up of parents and other concerned citizens. I would be willing to work a few shifts a month at each of the two schools that my kids currently attend. And I know I am not alone. This security force would have a coordinated response plan for a potential school shooting and possibly also for other potential incidents.
Anyone who argues that the result of the above would not be a net reduction in loss of life for our children is either an indoctrinated idiot, or someone who is willing to sacrifice the lives of our kids to advance their political agenda.