Alegrias1
I can see the issue you are bringing up about same sex families etc. Suzie If schools want to discuss facts and the accepted norms of today's society, as part of science or any other lesson, and parents or children object to that because of their religion, then the school should not allow religious prejudices and anti-science to prevent the discussion.
But, if a school or one of its employees goes out of their way to do something that is inherently inflammatory to a particular religion or belief system, as a way of discussing the differences between religions, that is over-stepping the mark.
If these parents had been protesting against having depictions of same sex families in school books, for instance, then the headmaster would not have supported their complaint, I expect.
Galaxy I wouldn't have any discussion of religion is the classroom. But you probably guessed that 
But I honestly don’t think you can divide issues up as neatly as that. What about discussions on the development of the rights of women in society for example? I also think you maybe overstating the behaviour of the teacher as ‘going out of the way’. I accept that amongst the Muslim community there are a hard core of fundamental extremist looking for something to be ‘offended’ at and if they win this one, then what?
As for how the same sex issue was dealt with a couple of years ago, I think some heads were hung out to dry - I’ll go and read up on it before I say more.