we met with his headteacher who does not seem positive at all.
I have coached my daughter last year who is going to BGS but my son does not seem on the same level...
Without wishing to spoil your Monday, those two statements leave me wondering whether he is GS material? Do you have CAT test results for him? Do you know what SATs levels he is currently working at? Or a reading age score?
I think it might be worth taking a step back and evaluating what you know about him academically before hiring a tutor. It is also worth evaluating his test results by question type as you go along because it may be that he has difficulty with specific types. That sort of problem can be addressed by tutoring. However, if the errors are more scattered, it may be that he is not going to grasp it.
I enquired Susan Daughtery but she seemed to want the full amount of money considering he will only be entering the course half way.
Not good at all ... Susan's class sizes are around 20, and that is unlikely to work well for a boy who might need more individual attention. Large class sizes tend to be of most benefit for children of fairly high innate ability who just need to be introduced to the method and techniques involved in VR.
There are some tutors listed here and, even if they are fully booked for regular tuition, perhaps one of them might be willing to do a one-off assessment that would give you a better idea of his potential? http://www.elevenplusexams.co.uk/servic ... /18/tutors
Please do ask for more help if you need it.