This story is dead on. I know this from personal experience and from teaching my own children. I could not add until I was 10. It was painful. I still remember it vividly. Suddenly everything clicked, and I rocketed through all the material I was behind on. I have six children, five of which are old enough to be in school. We have been home schooling them, I believe I have some creds on this. Two of them (both girls)…
Just adding my own experience to this: Until the age of 15, maths was considered a real "problem subject" for me. At every parent-teacher conference it was generally accepted that I would never be good at it (and I had no problem with that at all - I found the whole subject very boring and difficult). Then one day, at age 15, a classmate showed me how to do quadratic equations. I have no idea why, but that day a real…
From that point forward, however, math just seemed like rote memorization without any meaning or elegance. I shied away from it for years, only just returning to school to learn more math recently, in my 30s. I still feel like there's something fundamentally lacking in the way the whole math curriculum is set up, as I didn't see much that I really enjoyed in the period between 9th grade Geometry and Calculus II. I understand the need to build a solid foundation before learning more advanced material, but it seems very one-sided when there is such a breadth of interesting material out there.