Children often act up in a response because it gets them attention. A young boy who is now attending school now doubt is trying to develop his social skills and he might be falling into the trap that if perhaps he doesn't feel as smart, or funny or athletic as his peers that acting up will get him attention. Children crave attention from their parents and from their fellow youths and generally will do anything to get it.
While I certainly am not suggesting he's not getting it at home, as you had stated he was getting bad at school, so perhaps it is the fact that he is nervous, frightened about school and therefore is acting up to get attention, realizing that it works and therefore is acting up now at home. He might not understand what good vs bad attention is yet afterall, the negatives he's recieved are... what... no video games? Sure for a 6 year old in his generation that might seem harsh, but a child's imagination to entertain himself outweighs any video game.
The longer that he continues along this path without consequences the harder it will be for him to break the pattern in the coming weeks. Reasoning/Talking to a 6 year old, at least to me seems to be useless especially a 6 year old boy. You do need to talk to him about it, absolutely but talk alone will not change much of anything
