To clarify what I meant was evidence of the school's performance (not the facts that my child attends it).
I think it's useful to have a context for being in the 'top set' or on the 'gifted and talented' register (if such a thing still exists). After all, the top set in one school could be very different from the top set in another.http://www.elevenplusexams.co.uk/appeal ... cation#b43
However, I wouldn't burden any panel with, for example, an Oftsed report. Ideally, information about the academic calibre of the school would come via a brief comment from the headteacher. In the case of an independent school, see 2c:http://www.elevenplusexams.co.uk/appeal ... cation#b48
Panels normally have [anonymised] details of 11+ results for the school in question (if it's a Bucks primary or partner school), and this will give an indication of ability - if not of curriculum - levels.
On the other hand, there will also be parents arguing that their child's 'borderline case' should be looked at in the context of a school that has faced enormous difficulties, and that what has been achieved is against all the odds.