Thank you for your thoughtful responses. The school is quite large and I think there are about 5 classes per year, with 17 - 20 children per class. It is a well respected independent that produces great academic results.
My son has also passed the 11 + for the same north yorkshire grammer that hermanmunsters son goes to, but we live out of area - (shipley), so I am not too hopeful that we will be allocated a place there, which is why we entered him for the (local) independent. He did so well in his entrance exam, and came in the top ten, much to his and our surprise, and I do believe he would be challenged there. But - not if there are discipline issues. I feel hopeful that this was just the one class, and he was unfortunate enough to be with that class, but obviously I am very concerned. In the event we accept the place, they are in the year above, so not his cohort. One of the reasons we thought of going down this route, is that he loves learning, is smart, but can also be influenced by his peers. Plays the clown a bit at his state school to fit in with the 'footie' crowd, but actually is really motivated when he is academically challenged.
Your suggestions are very helpful. My feeling is if we are to be paying for his education, I want to make sure that it is the right place for him, and that my concerns at this point are addressed in some way before we accept a place.