CC6,

Although he is only 6, he is mature enough. So tell him that school is where you learn social skills and not just academic skills. When he grows up, he would be working with others and the kids learn to be team player or team leader and those lessons will help him become a CEO (of fortune 500 company) one day.

Just one of those answers I gave my DDs.

He definitely needs to move to 1st grade but preety soon, it will come back to this stage again. We did some supplementing at home until they are 4th grade.

My DD would read her books after she is done with her classwork or the teacher is busy with one on one teaching on some kids who did not understand the concept. (1st-3rd grade) She was never shy about her abilities and she would bring in her 4th grade Singapore Math book during 2nd grade class and do it when she was bored.