Welcome to Appeals!
For general advice I would suggest reading the Q&As, if you haven't already done so:http://www.elevenplusexams.co.uk/appeals/
...... after passing all his mocks and being an A student at his school
I doubt that an appeal panel will take 'mocks' into account.
Also, it's not clear what exactly an "A" student is, because it probably depends on the standard within the school, the percentage who get an A, and what is being measured (achievement or effort?).
The main focus should indeed be on academic evidence, but the following might be a better guide for what is needed:http://www.elevenplusexams.co.uk/appeal ... cation#b11
he was 7 weeks prem
Not sure I would pursue this point, if simultaneously arguing how well he's been doing ("an A student
he has very recently been diagnosed with Aspergers ......
Certainly worth mentioning,
although the admission authority can argue that they made reasonable adjustments/arrangements. (Edited - sorry, I overlooked that the reasonable adjustments were for Tiffin only.)
Probably best to express your appreciation of what was done, but gently try to point out that it isn't really possible to compensate fully for the difficulties faced by children with aspergers etc.