Why wouldn't a ban on headscarves fall exactly under Tinker v. Des Moines?

Because the "headscarf" is Hijab - a practice that some orthodox Muslims consider to be mandatory under Islam. It is not symbolic speech as addressed in Tinker. In fact, the hijab is not about symbolic speech at all.

Back up a sec. Just because something is mandatory under a religion makes it not symbolic speeech? Couldn't something be BOTH?

For example, in my religion, it whenever I see a girl reading "Cosmo" I must wear at least one article of clothing which says something quite sexist. (My socks say "repeal the XIX"). Under my religion, I do not have a choice! Now, maybe this is not symbolic speech, but does the fact that it is mandatory make a difference?

Taint and Joshua are right. Tinker should control this case -- it really should be open-and-shut, unless the state/school has some compelling interest in suppressing hijabs I haven't heard about.

As for the "it isn't symbolic speech" question: praytell, how are we supposed to draw that line?

I've now read the article and a couple other things (always better to do that first, I suppose) and I've changed my mind: absent evidence that the school is particularly targeting the hajib, Tinker doesn't probably doesn't control, and the school can probably do this.

At the same time, however, I stand by the comment that the disposition of this has nothing to do with whether the headcovering is "symbolic speech" or not.