I've been trying to find a study (I read online some time back) which showed siblings IQs don't correlate so well at age 4, but they do correlate very well at age 12 and 18. I find it interesting because only one of my three sons appeared extremely gifted at age 4. My oldest has a significant disability (autism) and my youngest just seemed to me more average (not disabled but not unusually bright either). Now that youngest is 8 he has "taken off like a rocket" and we now know he is very, very bright too. My oldest (who was thought to have mild MR as late as age 5) now beats me at chess (all the time), and may turn out to be the most gifted of the three. He writes and his writing has been picked up by international political groups (they have no idea the author is an autistic teenager).
One significant issue my kids had which somewhat delayed reading competence was a lag in development of their visual tracking. Intparent, your kids might have had something similar. When the tracking ability reaches the needed level, reading takes off.
On a related topic, I know there is ongoing discussion and debate about how early development of motor skill in early childhood does (or does not) predict giftedness. I have a friend whose father was a famous athlete (baseball). His grandsons acquired the ability to zip up their jackets (joining disconnected ends easily) and other similar fine motor skills amazingly early. My friend also noted that her nephews at at age 2 could hit balls pitched in their direction, and while my sons STILL have trouble hitting a ball with a bat, these kids really could do it easily at two. There ARE different gifts, and not all are interchangeable IMO.
