Firstly, he got full marks in the Maths paper used for secondary selection. About 2500 children sat the paper that year. One other got full marks.
Secondly, when he was in Y6, he was given weekly 1:1 Maths teaching by one of the governors, who had just retired as a secondary school Maths teacher. He told us that he saw DS2's level of ability about once in a decade.
Due to SEN, DS2 is seen by a child psychiatrist and child psychologist at a NHS specialist centre for children with complex neurodevelopmental conditions. They have done various assessments and it was there that I was told that his IQ / cognitive ability is somewhere between the top 0.1% and the top 0.01% of the population. This was not specific to mathematics, but that is one of his stronger areas.
The only reason I commented on this thread in the first place was to share my experience of a child who has been given a target of grade 9 for the new GCSE.
I am not a Maths teacher, but I do realise that this is a new syllabus and that students won't even be sitting the first papers until 2017.
I think that teachers have been put into a very difficult position with the specifications being accredited at the eleventh hour.
My impression from the Maths teachers on this thread is that a grade 9 target is ridiculous and arbitrary. My impression from the Maths teachers who teach him and have taught him is that grade 9 is a reasonable target for him to aim for.