I wish my daughter had that problem! She has verbal apraxia so she doesn't say much that's intelligible. I wouldn't worry about it, he's probably just excited. Also, perhaps he's really smart and the work bores him. He may be ready for something beyond what they are teaching him. Just something to look into. :)
He's only been in school for what - two weeks? It takes time to change behavior. I can tell you that most of this change will have to come through the school. He is too young to carry over stuff he does at home to a situation at school unless you can make it very close to the school type of situation.
You might try reading some of these books to him from the Learning to get along series. The listen and learn would certainly be appropriate - it can be found here - http://www.amazon.com/Listen-Learn-Learning-Along-Book/dp/1575421232/ref=pd_sim_b_1
There is also the Know and Follow Rules book which you will see at the bottom of the link.
These books are meant to be read several times and then of course to try and follow through at home what they illustrated.
How did he do in Kindergarten?