my dd is similar, she has really struggled with friendships. at nursery she was very popular and most children found comfort and strenghth in her strong personality, but that has been different at school, she has at times been very overbearing and most children dont like that and unfortunatly sometimes she picks up on this and goes to the complete opposite extreeme. It is very difficult, because whilst I dont agree and advocate the strenghths approach where children who are struggling with friendships should bear the responsibilty, but where my dd is concerned I do try this along with raising any concerns with the school, as I think that a relisiant approach is, rightly or wrongly a good thing to instill.
I have gone from inviting other children around to play in a measure to strenghten frienships, but that at times has failed, so I now tell my dd that it is not important to always have friends at school and the emphasis is on learning, but rather than seeking out the children who she aspires to be friends with and isnt always reciprocated and to now make sure if she is on her own in the playground and she spots another child alon then she should incluse them and attempt to build a game together.
according to my dd there are a large number of children in her class who also have no one to play with, I find that a little sad and surprsing that the play ground helpers dont seem to do much to team up children at play time.
I have always found talking to the teacher a little useless at times, because they assure me in class they do not see this and are not able to truelly observe what happens in the play ground.
Is your ds particularly bright and doing well accademically as I find that in my dd she has a very clear worth ethic in class and is not easily distracted and she is a bit of a high achiver, im not sure if this does truelly aftect her but I think it has its connections. I can also relate this to elevated anxiety in my dd that over spills into other areas, she is very hard on her self and I have only bagn to really see how this affects her in other areas. I think lots of reasurance and praise is the key and if you ence he is sad let him know he can tell you anything, and dont push it if he does not tell you things, if some thing is troubeling him it will eventually come out.