I agree with Guest55 send in the form saying with details to follow.
However I hope I can help you to learn from a mistake that I made - I did this but also sent in a covering letter giving some bullet points as a precursor to what I was basing my appeal on. This was a mistake. They give the appeal panel all the information that you send in even if it has changed, in chronological order. My covering letter and bullet points were put on the front of the appeal pack which was very confusing for the panel. I managed to get this removed and put to the back on one appeal but not for another and I am sure that it affected the panel's decision as some of the information on levels had changed. The panel seemed to think that things had been made up because there was discrepancy in levels. They thought I had doctored a form and wouldn't accept that it was an earlier copy despite it being dated.
I suggest that you say nothing except information to follow.
Eccentric, sorry about your experience. And thanks for sharing it. I will go with short but sweet, then. I was thinking:
We are appealing the decision that our son is not suitable for grammar school on the grounds that the Selection review was not carried out in a fair, consistent and objective manner. We believe him to be academically capable of thriving at grammar school and will seek to show this through academic evidence. We are also keen for him to attend the school for [reasons I have yet to think of].
Is this ok?