Delurking since I'm also in the UK with a 4yo DS who has just started school. So Hi :-)
I am a mathematician by training, so finding DS mathematical things to do at home has not been a problem: maybe it might be helpful to talk about some of the things we do. (Of course, maybe you do them all already, or maybe they wouldn't suit your DS.) Ours loves Geomag - lots of talk about shapes, how they're made up, their properties, e.g., regularity or not, comparative rigidity. Euler's law! (Some friends lent us the Sir Cumference books - they are perhaps not easily available in the UK (the friends got them in the US I think) but DS has enjoyed them, and that's where he got Euler's law, which grabbed him.) Kaleidajewel mosaic fridge magnets - again, shapes, properties of shapes like kind of angles, parallel sides, etc. Making solid shapes from nets. Tessellation. "The sum game" where you alternate asking one another sums I expect you already do, but have you tried "sums with a secret number", like "The secret number is called p, and the clue is that p - 2 = 2"? Squaring, and on to imaginary numbers. (DS introduced himself to a schoolmate the other day with "Did you know the square root of minus one is called i?" - well, I suppose it was efficient in the sense that it might have elicited a positive response, and then he'd have known he'd found a likeminded person!)
Science? DS has various science books that he loves, especially ones with experiments in, e.g. this one:
http://www.amazon.com/My-Big-Science-Book-Step/dp/031249176XMagnets, etc.
School-wise, here's hoping things will improve once they get to know your DS better. No real advice, except to be both polite and proactive... We're lucky in several ways: DS's teacher seems great, and his school has very small classes (independent). Also perhaps fortunately, reading is where he's obviously ahead of his age (far more so than he is in maths: while my DS is getting interested in multiplication and division, for example, I couldn't really say he can do them yet): his teacher did notice this on Day 1, and while he's been bringing home books which are not at all challenging for him in the mechanics of reading, they do have stories that he finds interesting, which is enough for now. He doesn't seem to have done any sums at all at school yet (so yours may be doing better there) and he does wonder wistfully when he will, but generally he seems to enjoy school a lot. His fine motor skills are not advanced, maybe even a little behind the average, so writing is a big challenge for him at the moment: I tend to feel that provided he's happy and he has one major challenge at school, things are OK. Sounds as though your DS doesn't have a serious challenge at school at all at the moment? Perhaps once they get the maths differentiation going that can be it? Here's hoping, and I'll watch for your updates with interest. If not, are there other school options available to you, or is home education a serious possibility?
