Florida is better than other states, but here in some cases, the judge will overlook the weapon, because it was used in self defense. I've read cases where illegal guns and switchblades were used, but no charges were made on the victim because they were strictly used in slf defense. This is by no means the rule, but most judges (at least here) tend to favor the victim. Also check your laws on carrying a pocket knife, some areas have length limits (ie under 3" blade length)
I would not say go around concealing an illegal firearm or weapon, but if you are on the fringe, and were truly in danger of your life with no other option, use whatever you can to defend yourself and save your life.
You may hear someone state "better tried by 12 (jury) than carried by 6 (dead)", but its never that cut and dry. Especially since you are not an adult. If you are under 18 (16 in some areas) you'll probably be in less trouble, but you still dont want to be in ANY trouble. Your best defense is to actively stay out of bad scenarios, and run whenever possible to get out of the scenario. Pride will kill you or worse put you behind bars until you are in your 30's! If you ever got charged with carrying a weapon (depending on your state) you may never be able to own or legally carry a firearm, just remember that.
Personally, I think mace would be just as good an option, and be even less trouble! Some states also allow stun guns (if you are a student in florida, both are allowed on campus for defense only, but legal for students to carry, so check you local, state and school laws).
I totally agree with 22 rimfire as well, in these days if you get caught with a knife at school you are in a heap of trouble and will get arrested! I went to school in the 80's/90s which wasn't that long ago, but if I took a knife to school, and got caught they took it away, and that was about all. I think they took away 3 from me, but I ended up getting one back at the end of the day to take home and leave home. Its not like that today. If you take a knife today you'll get arrested, a huge record, and possibly lose you chance to ever own a gun! I dont know your school or state/city laws, but I know if you got caught with pepper spray, you'd probably be in alot less trouble as long as you used/kept it responsibly! Go to a local police station and they should be able to tell you if you can carry a stungun/pepper spray around town, and also if you can take it to school.
Lastly, buy a good all steel/titanium mechanical pencil or pen (like cross) in a pinch it could be a very effective weapon as last resort, and the school would probably have no problem with you having it! I'd never refer to it as a weapon, or brandish it to your friends (pretend to use it like a knife/shiv), but if the time ever came, you could rely upon it if nothing else is available.
PS - I've carried a knife since I was 8, and is mostly a tool more than a weapon. Its a really personal weapon, and you have to be really committed to using it. I've been in a fight before with it. I sometimes have nightmares where are I am in slow motion, almost bound and cannot move. I try to fight back, but I am loosing the fight and its really personal. I wake up with every muscle in my body tensed up and cramped, and I'm in a pool of sweat with my heart beating 200 beats per minute. Its a scary thing, and was nothing like the actual fight, but is a recollection of all the fears I had in the situation. Its nothing like you see in movies with all the glory and fearlessness. I was lucky that the situation diffused because of people intervening, with only a few gashes and no real wounds for either of us (save 2 deep cuts to my arm - took weeks to heal and I sutered it, its always a reminder and will always be there), but there was a point where it was primal and something I would definatly not want to be in again. Some people have been in much worse and have alot more experience in this, but my 'fight' was the scariest thing I''ve ever confronted, and haunted me ever since. I havent had any knife training or anything and felt totally unprepared and very raw (it wasn't as smooth and natural, as I imagined it would be, or as I practiced in bedroom like it would go. It was sweaty, my heart was beating in my head, cold blood was tickling my arm as it ran down and I could see the triangular yellow fat globs in my arm in the gashes). It was nasty and like hell. Your best defense is to swollow your pride and walk away. If there is no other option you need to stand your ground, but make sure there is no other option.
Just my 2 cents