@PotomacBobThe great thing about "pepper spray" is that it can be whatever you want it to be!
Everyone knows what a "laser" is, and what it can do. But did you know that a "phaser" can be set to "stun"?
Pepper spray might be made from peppers, or it might be made from stuff that is made from peppers, or inspired by peppers, or it might just be "tear gas spray" or something totally non-pepper-adjacent.
Because if its relatively unknown chemical make-up, it might be nonfatal. It might kill people with asthma. It might kill people with lactose intolerance, or dark skins, or those that are sensitive to melanoma. Anything you want! Kill 7 bad guys and let one survive to swear revenge? Sure! Kill 1 bad guy and let 7 barely escape the cops? Also sure! Kill nobody but make the inside of the van really stink? Check!
I am a bicyclist. I have been attacked by large domestic pet dogs (of the type favored by low-income single young males) while on my bike. My state (in the US Northeast) regulates possession of pepper spray, by volume. So I could buy "small" canisters off Amazon but not big "bear spray" canisters. Of course, I could buy a case of 40 small canisters at once, and that would be legal and also cheaper, because laws + Amazon = weird.
I bought a 3-pack, and when I got them I immediately used one for testing and familiarization purposes. (And because I'm a not-so-young male...)
The particular model I purchased features a spray canister with an attached split-ring "key" ring (you know the kind: two wire circles jammed together to put keys on). At the other end is a nozzle with a "safety" trigger. The trigger is just "push down on this entire end of the cylinder". It's not like a spray-paint can with a tiny button, the entire cylinder end is the trigger, except:
* There is a "rim" around the outside of the trigger that just continues the wall of the cylinder. You have to push down inside this rim. (To prevent simple purse-shoves from triggering it.)
* There is a rotating tab interlock. A tab sticks out of the push-button, and you have to rotate that about 45 degrees or so to unsafe it. (You can carry it "unsafe" if you like, and I generally do - while riding. I unsafe/resafe it as part of my pre/post ride checklist.)
* The trigger depth is non-trivial. You have to go down at least 2mm (3/16ths of an inch) to fire. Presumably to avoid in-pocket discharges.
The problems I observed for my specific canister were that you have to think about what end to grab, and make sure you have the nozzle pointed the right way. The shape of the canister doesn't help with either of these things. The weight doesn't help with either of these things. There is the real chance of an accidental self-spray or of drawing out the spray with the canister upside down.
My experience with dogs is that I spray when dogs pursue me on the bike and moving, or when they growl and feint charge at me when I am still. In both cases, I shoot at the ground a couple feet in front of the dog, once.
Three times that has worked. The dogs generally either swerve away or turn back and walk/trot off. One time that didn't work, the dog pursued through the shot, and I escalated to a direct shot.
I am neither little, nor a girl, nor in school. I haven't had to use this on any humans that won't take no for an answer.
My particular product fires a "stream" not a "spray." If you have a "glass cleaner" (windex) bottle with a twist-adjustable nozzle, you can see the difference between spray and stream. Standing on the ground, I can shoot pretty accurately to the ground about 12 feet away. It is a continuous stream as long as you hold the trigger (until the gas inside wears out). So with a good grip it is very easy to adjust fire.
One risk for a "small high school girl" would be the magic button problem. If she "spritzes" with it, instead of holding down the trigger, she will likely miss, alert her assailant, and produce a tiny result.
You asked about the legality of pepper spray in schools? Others have answered, and we all agree. In 2022 it won't be authorized in any US school. It may or may not be legal, but it will be a policy violation or whatever. It's more likely to be legal where guns are more legal, but nobody with any sense would trust a teenager that would be willing to dump a cooler full of ice on their own head for internet points with a chemical weapon.
In terms of prep time, the worst case scenario is a woman with a big purse who threw the cylinder in because she was asked to. It's in there, she has no idea where, and she has to fumble past 2 tampons, a makeup kit, an extra pair of shoes, her BFF's favorite brand of maxi pad, and a cell phone charger to find it.
Once she has it, it's horror movie rules. You can make this part take as long as you want. You can have her hold it upside down, shoot herself in the crotch, turn it sideways and hit her defender in the ear, whatever you want. With the spray in hand, for the small cylinders, it's a half-second to confirm facing, two seconds to fix facing if it's wrong, then spray and hold for one second to start affecting a grown male.
If someone sees it coming, or expects it, and is familiar with resisting/overcoming the effects, you are back to horror movie rules. You can argue that its weak spray, ineffective against Marines, only takes effect when breathed in, only burns eyes, is the same kind that the Israelis use against Palestinian children so they grow up to ignore it, contains butane which is known to the state of California to cause cancer, is flammable, is explosive, causes explosive diarrhea, whatever you want.
FWIW, when training fighting dogs (illegal stuff, this is what Michael Vick got in trouble for), pepper spray is used. (Part of why I believe one dog pursued me through the warning shot.) A dog will be affected by pepper spray. A dog that has been trained to fight will likely "be affected" by becoming incredibly violent!