DS is 6 and in year 1.
I would say he has always been pretty confident with adults, but found it harder to socialise with children.
During reception he gradually became more outgoing and now plays with a wide group of children in his class and joins in at parties etc and I wouldn't particularly describe him as shy.
He liked his reception teacher alot and did well in class. Both her and the classroom assistant told us many times that he always had his hand up to answer questions, was very confident in answering questions and class discussions etc, but found it harder with the children. So basically their opinion of him mirrored ours pretty much.
At the end of the year we were really happy with his written report- the comments described the boy we knew and his academic performance (for want of a better phrase, given that it was reception 
) was really good, exceeding expectations in about five areas.
Fast forward now to year one. Generally, he seems happy.
His teacher seems pleasant. A bit less smiley and nuturing than last year but pleasant.
He goes in happily (which he didnt always last year) and about 8 times out of ten he comes out happy. However, at his open evening in Nov a few things concerned me.
She commented on his lack of confidence in class in dealing with her- this blew me away as it was so different to last year, when his confidence and willingness to join in was commented on many times.
When we met her, he sat a few metres away on the carpet with DD and looked at books. When teacher gently called over to him to ask him a question he noticeably jumped and looked nervous when she asked him......this really surprised me as her tone was pleasant and he generally seems happy with school (and is v enthusiastic about the learning). DH thought perhaps he'd been day dreaming and thats why he jumped....
Last of all, he had his nativity this week. He had two lines which he did clearly and confidently (we thought). Afterwards she said to me " i was so proud of him, especially given his lack of confidence"....then she went off and i was left 
My concern is that she has a really different perception of his confidence to us. I know he is bound to be a bit different at home, but his reception teachers seemed to know the same boy we do whereas she is decsribing a different boy.
Is she intimidating him and making him feel less confident? Or is he changing? Or does she not know him?
DH now agrees that this is an issue and we should have a chat with her. She is approachable so we will do this. But I don't really know what I expect from a meeting. ....except that I don't want my DS to lose out because he is labelled as lacking in confidence. I would also say i dont think I am seeing him with excessively rose tinted specs. I was always aware of his shyness with children.
One more thing....we saw all his school books at open eve and it was all positive, no spellings wrong in weekly test, all positive comments about his work etc. And his homeowork is always marked well. But she said "i'm generally happy with his progress" - when we asked what she would want to improve she didnt say anything. Compared to last year when they said they were very happy and he was doing really well.
Apologies for long rambling post, but all advice would be welcome. I have to run now, but will look again tonight. Thank you.