This is my opinion based on my experience, and that opinion is, if you're going to be using the arm teachers/students/yourself argument, it doesn't hold much weight with me, here's why:
I have a background in law enforcement and I switched career paths a few years ago and am currently working in education at a major city public school. I still have my conceal and carry license, but I would never take a gun outside the home except to the range for practice (it's something fun I do with the bros from time to time). I've been in a lot of situations, at no point when I wasn't in uniform would a weapon have made a positive difference.
Conceal and Carry: If you've taken any weapon training you know it takes time to draw and fire your weapon.
Even someone trained and ready takes enough time to draw as it takes an attacker to move roughly 21ft. The question then becomes, when was the last time you were attacked by someone standing 21ft away from you? You could always fire on an attacker after they jump/rob/assault you (assuming they didn't take your weapon away in the process), but have fun explaining in court why you shot someone whose back was turned. Conceal and Carry is mostly a feel good measure to make people feel safe.
Arming teachers: I've worked at schools where a stern look and a change in vocal tone is enough to bring students to the brink of tears. I'm currently working at a school where 1/30 students has had experience with juvenile corrections before turning their thirteenth birthday. School is just a place for them to stay warm in winter and get a free lunch. These kids aren't the ones I'd be worried about concerning weapons in school, it's the hangers on who feel the need to impress them that would worry me. The ones who start fires, assault teachers, destroy property, etc... These are the kids who sit there all day long thinking of ways to raise hell. They're going to be the ones who try to get their hands on a school provided weapon. We already have one officer in the building all through the day, and two others that usually stop in while on patrol. These officers have had kids try to snatch their weapons before, and they will again. Remember, these aren't adults, sometimes logic doesn't even factor into the decision process.
What about locking the weapons up? Sounds like a good plan, until you actually work in an understaffed school where you're running around doing lunch duty, doing the bus line, directing traffic between classes, dealing with fights, injured/sick students/a myriad range of behavior problems and suddenly you're on the opposite side of the school from the weapons when you need one while every teacher/staff member/student in your path is freaking out, and you may encounter the shooter on your way. If the shooter attends the school, they'll probably know where the guns are and either a)steer clear of the area, or b)head straight for it.
Most active shooters kill themselves when confronted: False. More shooters get taken down by law enforcement. Not by much, however. Forty six percent to forty.
Source
Another note, in a high stress situation, your perception of the situation changes. If you've ever been in a violent situation you'll know that sometimes you miss people shouting in your ear because a threat had your complete and undivided attention. Officers entering a school to see someone running down the hall with a weapon in hand might be overridden with emotion and fire on an armed staff member trying to confront the shooter. Have fun keeping your job and your mental state intact after that.
Current teacher training (at least where I've worked, can't speak for everywhere) has teachers instructed to enter lock down mode if a code red alert goes out. Lock the doors, cover up the windows, turn off the lights, and wait for the all clear. With my background, that would be my plan regardless. There's roughly one hundred schools in my district, some of these schools lack education basics like books in the school library. I'm not sure where the funding would come from to train and equip teachers to confront an active shooter, but without a serious increase in the budget I'd put it super low on the list of priorities.