Yes, just imagine how security would change if a lot of people were being killed on airplanes...oh, wait a sec...As a former school administrator, I wish I could say it is that easy. Schools and school systems always do a cost benefit analysis for the buildings. When retrofitting a building there are so many things that need to be altered/fortified/reassessed. One thing we know is that school shooters learn from each other--- most acts are not just done with little to no planning. So, in the double door example, many schools have buzzers to let you in and then a buzzer system to let you in the second door. That said, if a shooter has a bigger gun, the glass will shatter giving the shooter immediate entry. Magnetic doors can be a great thing but once the magnetic door locks anyone in a hall or area has no where to go.
In case of a current or former student, they often can get into a school with ease as they know the ecosystems vulnerabilities.
Every time I see a thread that has school and shooting in it, I am reminded that we continually fail to protect the most vulnerable. Not sure why.
We should bless the people who died AND those who tried to save them. This is a horrific crime to grapple with psychologically.