Trinity,
Our daughter who turned 12 this month is optimally challenged in 7th grade.  She earns an A average, but not without effort.  I also think she drew a line in the sand this weekend when we told her that her brother would start 6th grade math.  She thinks that is great, but I got the feeling that he would not be welcomed by her if he showed up on the junior high scene yet.  
I�ve attended a few local seminars regarding gifted issues including sibling relationships.  Girls can be tricky and go �underground� around the junior high years.  Also, if one child in the family is considered the �smart one�, the other sibling/s may look for their own different niche such as comedian, athlete or �gasp-�mall girl�.  I have to look out for both children.  
Our DS10 (just turned also) earns excellent grades as well, although he doesn�t have to work at it much.  He reads constantly, swims, plays basketball, trumpet, and piano, participates in speech team and acts in plays and is also involved with a charitable organization.  I think these other activities satiate his internal drive pretty well right now.     
As I stated above, I do think we will have to get creative in 7th and 8th grade for math and science.  Not that we are currently offered anything different, but I�m starting to think that I want to keep him at current grade level with some differentiated accommodation through 8th grade.  The reason is that there is a particular high school that he would like to attend that only considers the top 2-5% of candidates as determined by an entrance exam.  
He is highly gifted, but he�s not at the tippy- top echelon.  I don�t know that he would be competitive with gifted kids who are much older.   
As far as his current 5th grade teacher, I don�t think she has any ill intent.  She is just more interested in managing the herd than any one �kid�.  She offers a great Social Studies/ History curriculum.  I really did laugh out loud when I read your suggestion for bringing baked goods.  I�ve heard that before regarding how to impress and influence teachers in regard to meeting the special needs of gifted students!
I�m glad your family and son have been so well accommodated and accepted at the new school.  It sounds like a wonderful environment for an advanced student!
v/r   
Diana