I don't post often on the site (usually only on threads that I may have some relevant opinions) but was an 11 plus 'first timer' last year.
Of course you are going to feel disappointed for your son . He put in the hard work and as his parent you can see that he is suitable for a grammar education.
You have been magnanimous with your support and congratulations to other parents on the forum and are allowed a wallow(good word wallow...... reminds me of hippos and mud).
Usually a 'wallow' in my household precedes a large glass of wine and a very determined mindset that can overcome anything and everything.
Remember (as posted on a similar thread last year) The cream always rises to the top.
I did post on another thread that my son was abysmal at VR (just didn't 'get' it) but passed the Slough 11 plus due to higher scores on Maths & NV. I hope this proves the case with your son.
I wish you and your son all the best with the 'slough' results