It's interesting how liberal's first response to tragedy is restricting freedoms, while conservatives tend to look towards opposite solutions.
If as a society we decided to make our school's as safe as we can in a free society, we could. I believe a good percentage of teachers and administrators would be happy and willing to train up. Local police departments could arrange for the training, both initial and ongoing programs. They would probably be delighted for the community involvement. The suggestion about vets getting involved also makes a lot of sense, especially if they had MP training.
What we will get is some liberal feel good non solution like a Brady bill, that our leaders can point to come election time.