I know you cant add additional evidence after the letter but do you have to play all your cards/arguments in the letter? My concern is that it will allow the school to see and prepare responses a long time in advance?
i understand we see the Admission authority's case 7 days before the hearing but when do they see ours? as we have to send our appeal to the school in April doesn't that allow then an unfair advantage to plan the responses?
This not a court of law. Realistically, the school will offer the same defence to all appeals, with normally a cover letter that explains the specific reason you didn't get a place - live further out than the most distant place, for example. They don't have someone sitting down and forensically going through each case point by point. Their basic case will be to argue why they are full and cannot take another pupil.
Sometimes they may respond to a specific point - they may say, for example, that you are appealing because the school offers dance GCSE, but they may reply that there is no guarantee this will be offered at the relevant point. They are not going to be coming up with responses trying to catch you out.
You, and they, may both ask questions about the other's case at appeal.
Please don't offer any evidence at appeal that you have not offered already; panels do not have to accept it. You can summarise your points in your submitted appeal and expand on the day if you wish, though if something untoward happens and the appeal ends up being heard on paper it's best to have submitted everything (it also gives the panel time to read and digest your arguments).
There is nothing to be gained by trying to spring an argument on the panel/authority on the day.
When arguing on grounds of subjects/clubs that the school offer that are not offered elsewhere - would A-Level choices be applicable for a year 7 appeal or only GCSE options?
Not really - even GCSEs are sometimes a bit of a stretch as they won't be relevant for 3 years or so and things change, especially with niche GCSEs that might not have much of an uptake. Focus as much as you can on things that are relevant now.
There is a lot of info regarding the strength of the LA's case in other threads - but surely 99% of the time their argument is simply " we are full". Maybe its my ignorance but what else would they bring to the table?
An admissions' authorities case will often use data in terms of size of classrooms, halls, science blocks etc to show that not only are they technically full in the sense they are up to (or over) PAN, but that physically they cannot fit any more pupils in rooms. They may also show SEN/EHCP data that suggest resources are already stretched, and say things such as lunches have to be staggered, it's not possible to have an all-school assembly, etc. They may refer to overcrowded corridors, no places for bags/lockers, etc etc.