I too was a child who didn't live up to expectations - but I had always know what my limits were IYKWIM.
I was waaaay ahead in maths and english in my early years and it was pretty troublesome.
Two incidents stand out. Being taken, mid lesson, up to a class two years ahead to select my reading book - the class my sister was in . Yes she still hates me - and BOTH the classes hated me, mine and hers .
And then my best friend Jane asked me to help her with her maths because I was finished and the Teacher made me stand on the desk and told all the class " Well everyone, here thinks she is sooo much better than you" I was about 8 years old.
By 11 I was the same as everyone else and life was much happier.
But if it makes sense _ ididn't stop trying or anything. I had just got the concepts early and the more complicated the processing became the harder I found it.
Just average now.
And , to confirm the fact that reading can be a "trick" rather than an indication of IQ, my profoundly ASD son can read really well but often cannot understand the concepts he is reading about. aged 10 he still doesn't really get verbal past tense, speaks in the thoird person and still doesn't 'get' death.
Don't really know what any of that is relevent too - but cleatly needed to share