How close is your DS to age 9? I found that DS had a 'mini-puberty' at age 9.
He just turned 8 last month.
But his "Dad-knows-nothing" attitude has been present since birth.
My work-around has simply been to have any ideas proffered by teachers. So far this has worked quite well, especially for "character-building" exercises.
Last week I tried to teach him a short-cut in math... which he characteristically refused to implement. The homework task took about three times longer as a result, with plenty of errors.
His teacher, helping him with the issue, offered the same hint a couple days back and *gasp* it was the best advice in the world. DS implemented the strategy, saved time, reduced errors, solved world hunger, etc.
When I asked him about it last night, he said, "No comment, Dad!"
Ha-ha on him. But as long as he learns & improves, I don't really care who the teacher is.