My son was just like that. When he was older we asked him why he never talked much to other kids while in kdg or to the teacher - he said he had nothing to talk to them about.
By the way, he graduates this Dec in the top of his class with a Mechanical Engineer degree. He was on highest honors all through high school (top5% of class) and has been on Dean's list every semester in college.
at 12:28 AM on Nov. 22, 2010