This has come up in my area as well, a couple of years ago. I did some research at the time, and some of the local Sikh leaders were interviewed in the paper. (There was also a case of a Sikh girl running away and being reported missing to avoid an arranged, forced marriage, but I digress).
The point these folks were making is that wearing the knife is part of their faith, and that part of their faith includes both having the knife available for self defense AND for the defense of innocent third parties who are attacked. Their faith tells them they must have it, it must be useful as a knife (i.e. sharpened) and they must be able to draw it and use it in situations their faith considers appropriate. They also rely on the teachings of that same faith to not draw it when not appropriate, but a physical barrier would violate what they believe to be their religious duty.
To your point about a safe place to learn as being the high level concept, I really don't have a problem with someone who is a member of this faith carrying their dagger to school, under the presumption that advancing in the faith to the point where the dagger should be carried goes along with the education on when it may be used and when it may not. From what I understand of that teaching it's in line with my beliefs - I have various weapons, I'll use them for defense but never for aggression.
My point, which I don't make very clearly, is that safety in the schools does not come from the absence of weapons in a student's clothes, rather, it comes from the absence of malice in a student's mind. When I was in high school, which was a long time ago, I would bring guns to school so I could go target shooting with my friends afterward. I'd leave them in my car, but it was a small private school and I could have had them in 5 minutes if I wanted to. But not a single person on that campus was at risk because I had those guns in my car, because I had no intention or desire to hurt anyone. But now we have kids suspended or expelled for bringing a small knife to school in their lunch because it's a knife, not because it's used to harm or threaten anyone.
Now, to be consistent, if the Sikhs wear the dagger because their faith requires them to keep themselves safe and defended, and the school allows it, there is no basis on which to deny any student the ability to carry whatever they feel they need to be safe and defended. So should my daughter be allowed to pack a .357 to school if the Sikh kids have daggers? If not, why? Can I say it's a religious belief? Sure I can - one I came up with this afternoon. It's my religion, don't you start persecuting me for being a religious minority!
Cult: A small, unpopular religion.
Religion: A large, popular cult.
My opinions, which along with $7.95 will get you a cup of coffee at any Starbucks:
--Don't worry about the daggers;
--Don't worry about plastic knives, water pistols, kids with Tylenol or anything like that;
--Get rid of all this "Zero Tolerance" crap and let people use their brains
--Allow teachers to expel kids who threaten or bully other students - whether with weapons, fists or words.
Yes, I feel better now.
