Where I have struggled with and where I seen regrets from my mother is when the child is right at the age cutoff... either be the youngest or oldest. My sister was the youngest with the age cutoff being the day after her birthday, and my mother still struggles 20+ years later if that was the right decision. They ended up putting her into all girls school for middle school because that was when the age difference was felt the most, especially on the social and emotional maturity levels. My mother herself was sent to school 2 years younger than most of her class... and she does not believe that was a good move for her because she felt so out of sync - not academically, but in every other respect - as her friends all the way through high school.
Before our kids were born, we were thinking if they missed the cutoff, we would not contest it (they missed it by a day or two)... but that has completely changed due to the issues we see already at 3/4 years with DS being too bored and unable to relate to age peers - instead, he rather hang out with the older kids or adults. Our next door neighbors have 3 boys - one his age and two older, and he tends to drift towards the older boys there too.
The giftedness did throw us for a loop and caused us to completely revise our plans. And so we now have to go through the private school route with both kids to avoid the strict enforcement of the age cutoff that would hold them back just because of when their birthday is.
