They did remove the bandannas. It's the T-shirts they refused to do, and were sent home.
That's a blatantly hyperbolic misrepresentation of what happened in the school in the original news story. Seriously, this isn't about flags. It's about some idiot kids who decided to piss other people off, and got told not to.
Yes, piss off other people by carrying their own flag on their own soil. Just like Mexicans are constantly pissing me off by carrying their own flags in their own country. You just don't get it, do you?