We had the same in Bucks with DD (who thankfully did pass) - her ego was very tied up with being "the smart one", top of the class etc.
Whilst she did pass with room to spare, it was humbling for her to see some of the other kids (including one who wasn't tutored) not only pass but get higher scores in a couple of cases. And if that wasn't humbling enough, actually starting at grammar school has certainly made her reassess what makes her her, if that makes sense. Whilst she's absolutely in the right place, and towards the upper middle of the class (at an estimate), she's absolutely not top of the top!
I think at some point everyone has to learn they're not the smartest in the world, and far better at age 11 than at university, I reckon!
I think the tougher lesson would be "sometimes really hard work just doesn't pay off". We have DD2 going through it next year, and once again, that's the thing I'm dreading most.
Good luck for Friday!