DS is one of the youngest in the class
A point worth making, especially if the school comments on increasing maturity.
he's consistently been working above level since Y2
How far above? Straight 3s at KS1 would be a good indicator.
and is in the top 5 of his class.
Depends on the standard of the class!
At the end of Y5 his level for all subjects was 4a.
He also attends a study group for English and Maths which he really enjoys and is working on material a 13/14 year old would be covering however not sure if this is relevant.
It depends what the 'study group' is - anything to do with private tutoring is unlikely to count.
I will be speaking to his teacher regarding his predicted SAT level. I know other's have paid for their child to be assessed however is this something we would have to do?
It's certainly not a requirement - but it might help strengthen your case if you have no other evidence of reasoning ability (such as CATs).