I think one of my biggest fears (with regards to dd's education) is not having a teacher recognize dd's giftedness. So I can relate to you feeling uncomfortable at the teachers reactions to your concerns at that initial meeting. You know what he's capable of and what an uphill battle to feel like you have to "prove" it to a teacher.
I think there is absolutely nothing wrong with addressing issues that are of concern to you. You should be able to tell his teacher that your son isn't challenged, is bored, etc. And I think the teacher should take those concerns seriously, not personally.
As far as the math is concerned; It is good that the teacher makes him show his work and catches ds's careless calculation errors. I wonder if your son is making those errors because a) its boring him and he doesn't care or b) he is going quickly and its not concerned with "how" he got his answer. Either way the teacher should not degrade him for it but I do agree that he should be correcting ds's errors.
There is no way I would stand for a teacher making a demeaning remark to my child. They're supposed to be the adult and its inexcusable. I would definately address that with him and the principal. As frustrated as your son is, even as his dislike is showing, it never excuses a teacher from making such a response TO your child.
Maybe others here will have some other suggestions as to how to handle this but IMO I would not let it lie as it is. Your son is unhappy and frustrated and you certainly don't want him to turn away from learning and from school in general.
