His academic performance has always been very good (now he's 5B with a very high reading age)
I'd recommend as wide a range of academic evidence as possible.http://www.elevenplusexams.co.uk/appeal ... cation#b11
The choice of schools is important for academic reasons, reasons of distance but also because many of his friends will be going to the 1st choice school. This is particularly important as our son need the support of his friends as he has long-term underlying health issues which requires good peer support.
Make sure all your reasons are evidence-based - getting medical evidence is presumably not a problem, but will there be evidence to justify "needing good peer support"? See http://www.elevenplusexams.co.uk/appeal ... school#c11
Appeal panels tend to probe and test the arguments being put forward!