I am now very concerned that the lack of such extra letters will make it look as though the school's support is *not* actually as strong as I believe it is intended to be! Can anybody provide any input on this; does it make a difference to have additional letters from the school?
No, generally speaking I don't think it does.
I had thought that the idea of the standard format was to ensure that the different styles of writing from different head teachers had less impact and to enable judgement on a standard setup... am I wrong?
In my experience the vast majority of cases were supported by just the headteacher's summary sheet. I don't believe for one moment that has changed, and I think what you're seeing on the forum are some isolated cases, not a representative sample.
Rather than adding up letters of support, it would make much more sense to count the different examples of academic evidence set out in the Q&As:http://www.elevenplusexams.co.uk/appeal ... cation#b11