IF there is no metal detector, they should still carry. In Oregon, teachers/admins can
... until some kid with a grudge (or a gun-hating fellow staff member) has reason to suspect a teacher is carrying.
Then, that teacher's life changes forever.
Worth the risk? Could be.
Personally, if carrying at work risked my freedom and a felony conviction, I might be inclined to leave it locked in my glove compartment, where no one could possibly know.
But, that's exactly what all the cowardly, would-be murderous bastards and the legislators who enable them are depending on every law-abiding teacher to do.