Can someone tell me why my 5.75 year old, previously very promising with numbers, has been totally turned off maths since going to school?

[gaelicsheep]

And what the hell I can do about it?!

I have tried games, workbooks, websites. Somehow he has been given the impression that maths is boring and difficult. I can only assume this is coming from school friends who are picking up those attitudes from their own parents. DS used to enjoy doing mental arithmetic games in the car. Now he seems unable to do anything at all beyond counting.

I would just back right off and forget it for the moment. After a break go back-just for fun-maybe he has worked out that you have an agenda and doesn't want anything 'educational'. Try something like chess.

They just go through phases, it's normal for kids to be really into something and then suddenly go off it. I doubt its attitudes coming from school friends who are picking up attitudes from their own parents, lol! My son at the age of four could name all the planets of the solar system and new loads of space facts. He used to watch Moonwalk One for fun. At six, he is not the least bit interested in either.
I wouldn't worry about it, if your son is going to enjoy and excel at maths, he will come back to it. Just do as exoticfruits says, back off for a while then try again in a low key way :)