Hi all, sorry I hadn't seen your replies! (Life gor a little more hectic - somehow!) Big response sorry -
@JaffavsCookie thank you for this. It is certainly a concern! Ill go through it again alongside Yarm.
@allthefunatthefair thank you for such an excellent breakdown and explanation of your experiences of both schools.
Our quiet but able child flying under the radar anywhere is one of our main concerns, along with bullying or being cast out for being a bit quirky and sensitive.
Cundall has such a fantastic feel to it. Really caring and the children seem lovely and really happy. I'm hopeful that they would be able to help DS succeed to the best of his abilities and build some confidence and resilience.
We visited both Yarm and Cundall (actually visited Barnard Castle too but decided its about 10 minutes too far away at 45 minutes. Really disappointed as that seemed to be exactly what we are looking for!)
Cundall seems to have the sports/pastoral/smaller size/lovely grounds/close to home but concerned that the infrastructure is in serious need of attention - very tired portakabins with single glazed or blown windows and bar heaters, rotten wood etc. There also didn't seem to be much in the way of science/technology provision until senior years which would be disappointing for DS.
Yarm was very impressive. Very shiny. Amazing facilities and clearly a lot of investment is continuously put into the school. Dedicated science labs, technology labs and ict suites from y3 were something I know would really suit DS. I, for some reason, cannot shake the feeling that our quiet and sensitive boy will find it all quite overwhelming and will be lost in a class of 22 kids/year group of 66 kids. I think he will try to do the bare minimum where it is easy to do so.
Right now I feel that Cundall suits his personality and will help him become more confident and find a love of learning and that Yarm, on paper, is academically and facility-wise unbeatable. (Easy to quantify something when facts and figures like exam results come into it - not so easy when you are talking about confidence/happiness/resilience!)
We have now had the discussion with DS to explain things and he is really excited about the idea. He is booked on for a taster day at Cundall (less overwhelming for him than Yarm and he can't wait) and a tour of Yarm prep in the new year.
The school he is at is a lovely school, but it really doesn't seem to be the right fit for him. With issues of ongoing physical incidents and lack of academic challenge for him we are sure there has to be a better fit for him. We are just so torn between the two schools as they are so very different and both bring completely different things to the table.
The identified safeguarding issues are a concern.
I'll update when we know more. Until the next steps I'll be constantly scouring the Internet for anything that might help us 
*We appreciate what a fortunate position we are in to be in this predicament and have considered our local state alternatives 