This gets at the debate about red-shirting.
I was amazed last year when volunteering in my (then) first grader's class how, after awhile, I could pick out the kids with the really late birthdays who were young for their age. They were not always the smallest. They tended to be very immature, have poorer fine motor skills, and were just sillier.
One girl used to randomly wander around the room- I would gently redirect her to her desk to try and write the little paragraph the class was doing. I finally realized that her birthday was in August, and she was almost a year younger than everyone. (I don't know if she was gifted or not).
At such an early age, K or first grade, you can see a difference in how they write or pay attention, simply based on age. I think it can make a difference too in how they do in school- if you can't sit still to write you paragraph, simply because you are way younger than everyone, then you will miss out on that academic opportunity.
