This has always been interesting to me as well. DS6 is a PG child. He did everything early and is constantly seeking more and more information and learning. Before he could walk he would crawl to pick out his favorite books off shelves and LOVED books. He was matching things before he could walk and would carry around things in pairs as he crawled...and was reading before 2.
DD3 is so incredibly different, but such an amazing little girl. She too enjoys reading a lot, but not as much as DS. She is quite creative, imaginative, and very expressive in every way. She is dramatic and very verbal. She picks up on things quickly, and wants to do really well at things. She knows all her letters and the sounds they make. She knows some numbers and can count objects and group them all. She knows her shapes (and definitely colors as she has to match her outfits). She draws pretty cool pictures, but she is not all that interested in letters and words and reading. She is much more into dress-up, princesses, telling elaborate stories, making things, drawing, and loves to watch TV. They play wonderfully together most of the time, but are oh so different. I imagine we will have her tested sometime, but am not in as much of a hurry since I don't think we will be requesting the K skip like we did with DS. DD goes to a preschool for 3yo's for 4 hrs a week and she doesn't seem to like it much. She likes it after she goes, but not when she is on her way. She does seem to have some friends there and she is quite outgoing (after her initial watching people being shy phase). I am wondering if she is just not connecting with the other kids as she does seem to prefer older girls to play with. She keeps wanting to go to her brothers school with him. Anyhow, it is just hard to believe how different they are....but I find it fascinating watching them each teach eachother things. She teaches him more social skills and he teaches her academic things