Makes sense to me to be prepared for something awful to happen. The mere fact that the school police will be prepared for an assault will help to deter such assaults.
Are you really that scared of someone shooting up a school (other then maybe a SWAT team during ‘Collateral damage’) to allow armed government guards at schools? Ya know, I grew up during the cold war and that is exactly what we were told to defend against!.
If the long gun is kept in the officer’s office and the shooting is elsewhere, like the gym all the good it will do is give the officer an excuse to flee the scene: I was going for my rifle,”. Not to cast espersions on officer’s in general, they are armed and will use their radio and side arm until maybe someone else shows up. Most schools don’t have multiple officers, maybe Chicago does, I can see why they would. What about arming the teachers? I had one coach who was ex navy and a golden gloves boxer. I expect he’d have been willing and able.