You could perhaps try an appeal where there would be an opportunity to talk things through with the panel.
You would have until the summer term to gather evidence.
Write to the headteacher now, thanking him for meeting you, and saying that you have understood that:
• The school is out of county so never complete the review forms
• They have a policy of only supporting those that have missed by 1 mark and will write a supporting letter in these cases only.
• His current year 6 teacher can't predict his end of year results
Keep a copy of your letter and of any response.
See if the Senco will give you a letter.
If there are any further incidents, such as bullying, complain to the school
in writing so that you have a written record.
If you can afford it, you might consider the possibility of getting an educational psychologist to assess your son to see if he is of grammar school ability.
https://www.elevenplusexams.co.uk/appea ... ication#b3I'm not suggesting any of this would necessarily work, but at least you might have some evidence for a panel.