I've made a few posts in the past about my DS who scored an L5A in maths when he was in Y2. He is in Y4 now. The school finally put together an IEP for him, have a secondary school teacher involved and he gets a 1-2-1 maths lesson once a week. For the rest of the week the class teacher struggles to give him material appropriate to his ability.
Stretching is a word that riles me. Teachers often expect a pat on the back for "stretching" a DS. They've had no formal training in the teaching of gifted children and, TBH, the average teacher doesn't know much even about teaching intelligent children who are not gifted - like my DS - but who are simply in the top 1% of ability.
That's going to get up some teachers' noses, but we've been there and done that before in other threads. They are entitled to their opinions. Some work very hard and go to a lot of trouble to "stretch" the "more able" but they have neither the training, the resources, the time nor the support to help these children achieve their full potential. The state system is stuck in a 1950s time warp when it comes to educating these brightest pupils.
"if his class is working in tens and units then he should ge working in hundreds, tens and units."
That's what they tend to do. It's the most unimaginative cop-out possible. What if that hundreds, tens and units is still far below the child's ability? They'd move him up to thousands and tens of thousands! In Y2 my DS was able to take million, billions and trillions, reduce them to powers of ten to make for speedier writing and find the square and cube roots to those numbers. But because he faithfully handed in the sheet of 14,000 + 16,000 = 30,000 type sums, he'd get a few more of those to practice on before they moved him to adding 100,000 + 200,000. They did not even know what he was capable of quite simply because they never asked him. Ridiculous. In Y2 we had to go in, see the head and complain before they agreed to test his ability. They put him through a KS2 paper and were dumbstruck when he scored what he did. How can an OFSTED outstanding school have a child for three whole years and not know what he's capable of?
These children need to be learning at a speed that's right for them and determined by them ....and that speed is quite a hectic one. Studies have proven that the best results are achieved when these children work with other children of similar ability. At least your school seems to recognise that. You're rightly identified that Y6 may be academically well suited but the wrong social group. There is another problem with this accelerated curriculum.
The good schools, the very good schools think they're doing the DCs a favour by teaching them more material from the curriculum. Why? Because they haven't the vaguest idea of what maths they can teach from outside the curriculum and teaching from the curriculum is easy - simply get a teacher from a higher class to provide the material. These DCs need to keep learning, but pushing them up the curriculum creates problems for you and the child in later years.
Sorry to say this, but if your DS is as you say he is, there's almost nothing the school can do to cater for him appropriate to his ability. But there's a lot they can do to give the impression that they are.
idratherbemuckingout has what's probably but sadly the only solution.