Honestly it depends on the school and state laws here in kentucky the law is a 3 inch blade is allowed but its still up to the school if they want to let you have that or not have one at all. At my highschool becouse of where it was and the small farming community everyone carried a pocket knife and we used them in the shop. i had a pocket knife with a 4 inch blade and the only people that really say anything about it were the real pricks and even they disnt do much other than say thats not under a 3 inch blade but never really did anything about it in citys id say you might get suspended a couple days b/c they dont generallylet you carry a knife at all
If you're caught with it in your possession with no suspected attempt to use it for harm and you are under the age of 18 the worst thing that will happen is a short time in juvenile detention. However, most circumstances will simply call for detention or suspension, along with seizure of the weapon.