Mrs Duck: the 'problem' with Miss or 'Mrs' is that I don't think whether a woman is married or not needs to govern the title she is given. It shouldn't matter in such circumstances whether one is married, in or out of a relationship, in or out of several, gay, or celibate for that matter.
'Ms' is unoffensive, unubtrusive, and makes it clear (on written material for instance) that the addressee is female. It puts the emphasis on the woman's name, not marital status. I think that's an important lesson for young people to learn in itself.
I worked with young people in a theatre context for some years. With most young people, we had a time convincing them that we didn't like to be called by a title, but that our first name really was preferred. While I understand why such a barrier might be desirable in a formal school context (although I cn think of plenty of reasons why it wouldn't be - it's just that we're used to it by now), we were aiming at a very different kind of education. The kind of theatre we were producing relied on a COLLABORATION between adults and youths. It would have been damaging to that power structure to have the kid call us "Miiiiiiiiiisssss!" or whatever.
In Australia, the correct way to address a formal letter is not to say "Dear Mr Bloggs", but "Dear Joe Bloggs". I say 'correct' because it's in the Style Manual that way, and I used to work with a book editor who had big tantrums when such style 'rules' were transgressed.
Callie
Callie