I don’t think it has to do with IQ levels either. Although I have a high IQ, 141, it is not world shaking(such as 160 to 180 or so), my brother has within 2 points of me but he had to learn reading the old fashioned way. He never fell behind but he didn’t learn on his own and went through the Dick and Jane books at the normal pace. I think there is much about learning that our educators(and those of the past)have yet to discover.
My son has a very high IQ, so I know it doesn’t have to do with IQ either. I do think some kids just read when they are ready to read.
What is interesting is that my daughter has a fairly low IQ because of a brain injury.
After she finished her special reading program, she really started doing well in school.
Now in middle school, she gets better grades than lots of kids. She is in honors math, and she had straight A’s the last quarter. (This quarter she has a few B’s, but she has been sick a lot this quarter.)