Anonymous wrote:OP here. Thanks for all of the feedback. My DH strongly agrees with holding her back as well. Some of my hesitation is that I was a late July birthday myself, but there was never a question of holding me back in public school in the 1980s and so it was my experience to be the youngest in the class. Funny enough, my childhood best friends all had summer birthdays as well and in retrospect we were all the same maturity-wise (and in terms of physical development, too!). DD is our oldest child, and it's so interesting to see how class room age cut-offs have shifted, particularly in private schools. Thanks again for the timely and helpful responses.
OP, I have a late August birthday and also test as PG. I was intellectually far ahead, but more socially immature than my classmates. Social acceptance is as critical as intellectual development. More so, I think, for long-term happiness.
Definitely hold your daughter back. Believe me, the intellectual development will be far easier to handle and address than the social development. Also, some very bright children have issues around sensitivity and intensity. If she is displaying any of those traits, she may need extra support from you and her teachers.