We have 2 boys, 4 & 6. My 6 yr old is very very smart, bright and active. He always did everything very early on however we have had behavior issues in school and at times with sitters. In school, gets up out of his seat without persmission, hitting and threatening kids, potty language, repeats everything that he hears from home! With sitters and new people, its almost like he is testing his limits, he will use bad languge, hit his brother very very hard at times, and again repeat family things. He is infatuated with "older" kids and thinks he is on the same level as adults.
He also refuses to sleep in his own bed. During May & June he went back to his bed!!! We were amazed but as soon as school was over, and the new sitter started, the fighting between the boys has gotten worse, and he is back in our bed. Even when we move him to his room, he wakes up and comes back. He also micmics EVERYTHING he sees and hears on TV or from others. My son loves to try on new personas! We really have to monitor everything that he is exposed to!
In the park, he plays well with others, a few times kids have come over to the sitter and said " he said bad words or he cursed at us". However, we have no problems controlling him, we go out to dinner, the movies, road-plane trips, theater, etc. with no issues. Yes, sometimes he will ask for toys, etc. the normal things but he is controllable.
I have taken him to see 3 (THREE) psychologist and they all said that he is fine and just getting bored in school, and regular sibling rivalry. He participates in activities like ballroom dancing, lego robotics and sports is mostly follows the rules. At times he will go off and do his own things, but I get no complaints.