In her view he is suitable for a grammar school because the structure would suit his personality. Does this make sense?
I asked if the ranking would/could be changed and she has said that in order to change his ranking she would need to reduce someone elses and she didn't feel she was able to do that.
Well, she's starting to come up with the truth - of sorts.
What I think is wrong here is that she has ranked him "3 - recommended with reservations/ 1 - Self starter. Independent worker. Consistent. Highly motivated." That is a long way from "monkeys around a bit, needs structure"!
She is talking tosh when she says that she would need to reduce "someone else's ranking" to change your son's. The schools do not have a quota or limit on rankings - if they have 20 children who are 1:1 standard, they can rank them all at that level, and the same goes for every other possible variation on rankings.
Heads have every right to change a ranking if they feel that the child has improved since the original ranking. In many cases the ranking will have been based on data from the end of Year 5, a whole 6 months before the Appeal, so it is entirely possible that their ranking would be very different by the time of an Appeal.
She is right that she cannot change the Order of Suitability, as I said before. However, she can
change your son's ranking and give an indication of where that would
have placed him on the original Order of Suitability.
Unfortunately what often happens is that a Head will refuse to admit that she might have not been entirely accurate when doing her rankings. It is a task that can require the Wisdom of Solomon, and it is only when a child suddenly comes so close and an Appeal is looming that Heads realise that they have to justify their decision for a specific child.
I would polish off the letter, mention the ranking briefly, if at all, and I would probably leave out the OoS from your letter completely. Focus on the academic evidence - reports, exam marks, previous test scores - all the positives that you have in hand. Then put your efforts into getting the Head to write a further letter of support next term.
You will also need to work on how you explain the "3" ranking to the panel - some ways will be better than others, and you will need to play around with the wording. I think that if you keep close to the Head you may get some more positive feedback over time.
Good luck - come back to us if you need to.