To the OP, you say that knives are "frowned upon", what exactly does that mean? If you get caught carrying a knife will you be expelled? What type of school are you talking about? I'm curious about where this school is and if it is a public or private school because I know that it is illegal to carry knives of a certain length on school grounds in many places. And by "illegal", I mean a person can be arrested by the cops and taken to jail or juvenile hall.
If you are in college, getting caught with a knife in violation of campus rules might very well get you expelled. And any money spent on tuition, books, etc, could be forfeit. That could be a pretty heavy price to pay just to carry a knife. And if you are expelled from a college for "possession of a weapon" (and that's likely what it would be called) good luck getting into any other college with THAT on your record.
If we are talking about junior high or high school, getting caught with a knife in violation of school rules might get you expelled. Then you have to find a different school that will take you or be home schooled. And having a school record with a "weapons violation" on it might very well prevent you from getting into the college of your choice, or any college at all. It might also hurt your chances of entering the military (if that was your desire).
In general- if the rules say "NO KNIVES AT SCHOOL" it's a good idea to obey that rule because you might pay a very high price if you get caught.
And if you don't think that you will ever get caught because the knife is "concealed", well, people never think that they will get caught doing things they aren't supposed to, but they do anyways. If you feel safe in taking out your knife to cut something, even discreetly, someone might see it and report you. Or maybe it falls out of your pocket or bag. Or maybe the school decides to do a random search for weapons. You just never know how you might get caught.
Now I like knives as much as anyone and recognize the value in carrying them, and I carry some everyday wherever I go. But I also recognize that violating a stated school policy can result in some very unwanted repercussions. I hope you will carefully weigh all the risks before you violate any school rules.