I can only partially endorse this message. I am an Old Boy from Tonbridge, albeit over 35 years ago. Sporting prowess was then paramount in terms of 'seniority' at my Boarding House. Now academic achievement has also been added to a list of pressures and measurements, although even then it liked touting its Oxbridge achievements. I think the new HM wants to reform, but perhaps with added pressures on children???
My honest feeling is that it depends on you to remain as loving parents, rather than take my own family's view that I was handed over solely into the sole care of the School. That didn't work for me, but that is my own experience.
From my own experience I have seen many non-sporty and non-academic Old Boys do well in later life. However it's something you just can't predict.
I think the school currently offers help for a son of your own description. Michael Heseltine is famously dyslexic and has achieved at the highest of levels in Public Life, although not an Old Boy from Tonbridge.
Tonbridge, as we know, is an expensive school - even Eton & Harrow are cheaper.
I know it's a tough call from you, but do look around. There are some amazing alternatives.
I'm so sorry this is such a tough call for you. But if you are asking the question, somewhere deep down you know the answer already.
I sincerely hope my message is of help to you.
PG