Ds1's teachers are on a job share. He has one Monday through Wednesday and the other Thursday and Friday (although strangely he seems to have the first teacher on a Thursday sometimes as well). 
Since half-term the first teacher has taken both myself and dh aside and told us that ds is being disobedient and defiant and generally being very difficult and not listening and concentrating at all. We were surprised to hear this, as all his teachers historically have said that he can be a bit opinionated, but he has never been defiant or disobedient at school before.
At the beginning of the year, she said she felt he wasn't hearing her when she asked him to do something. Yesterday she said he is definitely hearing her but choosing to ignore.
Her example was that she needed to speak to everyone at the end of the school day and asked the class to sit down so,
Teacher: "class, sit on your bottoms please" ds didn't sit down and was facing the wrong way so ...
Teacher again" "ds1, what did I just ask you to do?"
Ds: "sit down on our bottoms"
Teacher: "yes, so why aren't you doing it"
Ds: "I am doing it, I'm doing it now"
Ds sits on his bottom.
She reported this as obvious disregard for her request, followed by being extremely rude.
I have a feeling she isn't giving him time to process requests, particularly whole class requests, before telling him off for not complying. He has a tendency, when asked something, to roll his eyes and repeat exactly what you just said very slowly before acting on it. He has however, learned not to do this out loud around other people, so is most likely processing the instruction slowly in his head. Obviously he can then repeat it, but hasn't taken it in, so it appears that he is being deliberately disobedient. The problem here is that I get the feeling that she will just think we are giving him excuses for his bad behaviour. She has told me she knows very little about ASD (she read a leaflet the SENCO gave her) and struggles to know how to handle ds.
His other teacher has a child who was assessed as 'borderline ASD' herself. In ds's diary for the same two week period, she has written that ds seemed focused, cooperative and happy and that she was really pleased to note that he had been sociable, communicative, cooperative and happy.
They sound like they are talking about two different children (although the second one sounds more like the ds1 I know and love).
So how do I deal with this? Obviously the first teacher is struggling with him. She has said before that she cannot "allow him to be rude to her" as "the other children will copy him" and "it can't be one rule for him and another for all the other children". So I think she thinks his behaviour is undermining her authority. She is autocratic in style and quite strict, but he seemed to be getting on ok in her class until the half term break.
Its parent's evening tonight and his IEP review next week and I need somehow to get across to her that he really isn't being defiant or disobedient, he just needs handling in a different way. You'd think the teachers would have discussed this amongst themselves, especially as one seems to be able to get the best out of him and the other definitely can't. But apparently not. 
I have downloaded a few documents from the NAS site and highlighted what I feel are the relevant points, but I feel like I will meet with resistance if I give these to her to read as she is always telling me that ds is "only one of 27 children" and she barely has time to fill in his feelings diary with him as it is.