I would like to explore this issue of PG kids telling others that they are smart. We have the same problem with our 5 year old son. The problem is, he is very smart, like all the other children mentioned here. We want him to feel good about this and not ashamed. This goes along with all the other social graces he hasn't learned yet and we find ourselves apologizing for. I have tried the advice EandCmom has given about using the strategy that it will make others feel bad if they don't feel as bright as he is, but that didnt' resonate with him. He mentioned that we always say how great his cousin is in baseball and that doesn't make him feel bad that he isn't a great baseball player.
