A good point.
You cannot challenge the admission arrangements (so long as they are lawful and have been correctly applied), but you could make this a main argument under the heading "Reasons for wanting a place".

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Etienne

I really appreciate all the responses I have received.
I will try and draft something without being complacent about the allocation process and trying to use the points that have been mentioned. I can see that the whole appeals process is incredibly stringent.
With it being the first time I am going through this process, at the time I had thought that the biggest hurdle was for my son to actually achieve the qualifying score!! After watching the open day videos and looking at the website, I had assumed that generally all cat 4 students are offered places but I know that there are no guarantees.
I hope I have a strong enough appeal.
Thanks again