Reassure him how fantastic he has done and how proud you are.
My DS got all 6 and one 7.
He worked hard but he's also naturally clever and could probably have got 8 and 9s if he pushed himself....but that's not who he is.
And I'm proud of that. I'm proud he's calm under pressure and takes everything in his stride. He's well rounded , he's a kind and caring young man and very mature.
Your son needs to know that the numbers on his slip do not define him.
They are just the ONE route to the next step.
He could have failed and there would still be options for him.
I got A*s back in my day.
I obviously sat in the same classroom as those who got Cs when I went to college. We were all on the same page.
Top grades made no difference whatsoever!!
Also I was a whizz at languages apparently....took French A Level.and failed..I found it way too hard!
GCSEs are not everything!
I wish schools etc would stop applying so much pressure. It's silly.
Hugs to your son.