The concern I have isn't with gun control but competence. There is a lot of studies about effective armed response and fear. Last I read the police in the USA will hit a target in a firefight 20% of the time. The criminals have about a 12% likelihood of hitting their target. If we assume teachers will not have time to do specialist firearms training they will send lead into rooms and hallways crowded with children up to 80-88% of the time. I will be interested to see how this gap in competence will be met.
The other thing that has gotten lost with this deputy is that the US military has a lot of data on fear. Bottom line is there is no actual way to control it. Once you brain goes into self preservation mode you do not act rationally. Loads of examples of this.
So, I really question whether the deputy response was intentioanl in that sense when it has nothing to do with his training. But, also, he was probably not skilled enough to conduct a firefight in a hallway teaming with people. So I think things would have gotten messy if he tried to identify a 19 year old target in a sea of 17 year olds who were probably running around with bags and who knows what else.
From the studies whomever is carrying a weapon, and does not have active shooter training, will only provide safety in a very limited scenario. Certainly not in a complex school shooting situation. That's probably why in some 53,000 firearm incidents in 2015 only about 1300 where self defense situations. Most of the time it is better to leave it to the specialists.