It is true that some gifted kids pass many of the traditional milestones early but sometimes they don't or sometimes the clues are not so obvious as walking/talking etc. I think problem solving issues such as using objects to reach things, early learning of object permanence etc. are not as obvious to parents. Also I find that a sense of humor can be very telling as well. Humor requires advance knowledge in order to see the twist or comic "wrongness" of things.

As for reading...my brightest of children was not even reading as he started Kindergarten. However, in October we went on a trip and I brought some very early readers (The dog is big.) and by the end of three weeks he was reading Magic Treehouse Books and by December, Harry Potter. It was wild. I have four kids and all are very bright but that experience blew me away.

Kids don't necessarily progress in a straight line. I also find that the really bright ones get into a topic or area of development and really progress and then out of nowhere drop that area and pick up another. And THIS is why I don't understand how they can say these kids are fine in traditional classrooms where you spend 25 minutes a day on each subject. But that is a rant for another post. ;-)