I appealed for a place successfully. I found out how many students who had a place that had received less marks in the exam, than my little darling.( they got theirs through proximity, siblings being at the school, and association with the school, such as father's having been there) There were 31.
I got a superb Head teachers report about my DS. Imperative.
My DS did pass the 11 plus though. We didn't have much to go on, but on the day of our appeal, we were dressed up to the Nth degree ( suits, heels, crisp white shirts etc) and we were in professions and we are acknowledged as having above average looks. Who knows if that helped, but in he went.
Was your DS ill on the day or got special needs? Dyslexia ?
I am not sure you have any chance if your child actually failed the entrance exam. Also I wouldn't want to put them through the agony of not being able to keep up. The school that my DCs went to, would ruthlessly throw them out. As anything other than straight A's at GCSE would spoil their results. The grammar schools in Kent will be the same.
Other than that, could you send him to an equivalent Private school for three years and he could have another go at getting in, in year nine.
However, if they have support from a rock solid family, they should be fine wherever.
One of my SILs went to a comp ( failed to get into Grammar School) and has just been headhunted again and has nondescript GCSEs and bog standard A levels. He did get a first class honours degree from a bog standard uni and a PhD. But Jobs in I.T. Are different. He is on his way to being a millionaire. Luckily as my DD, his wife, who went to a very competitive GGS isn't at all competitive..
It is so stressful .... I feel for you, sorry I can't be more helpful.