Welcome to the forum!
If you need academic evidence in your situation:
First of all, will the current school co-operate with you?
• Will they put in writing that he is "
in the top groups despite being a year younger than most of his cohort", and that he has "
an advanced reading age"? (And will they define exactly what is meant by an advanced reading age?)
• Will they be prepared to say that his academic ability is "
above average", "
significantly above average", or "
outstanding"?
• If maths might appear to be a weakness, perhaps because of a different curriculum, can they counter this by saying how good his maths is?
• Is there any evidence to show that the current school has a really good reputation and very high academic standards?
Secondly, for appeal purposes, I wouldn't attach much weight to any assessment from a private tutor or from 'mocks' - but, time and money permitting, a report from a qualified educational psychologist (using WISC or BAS tests) could provide useful additional evidence, especially if the outcome is very favourable (i.e. results indicating
very high percentiles).
See:
https://www.elevenplusexams.co.uk/appea ... ication#b3If the grammar school is oversubscribed:
You will need good reasons for wanting a place - reasons that are strong enough to outweigh the prejudice that will occur if the school has to go over its admission number.
See:
http://www.elevenplusexams.co.uk/appeal ... -school#c2• In your son's case, this could include his interest in languages - but can you come up with some hard evidence to show that his interest in languages such as Mandarin, Latin, Swedish and German is more than superficial?
• Can you match your son's interest in languages with what a particular grammar school offers?
Is the grammar school noted for its foreign languages?
See:
https://www.elevenplusexams.co.uk/appea ... school#c34Does the particular grammar school provide many more opportunities for the study of foreign languages than the non-selective schools?