Both my girls were repeatedly tested and determined to be reading at a 12th-grade level while in 1st grade. Obviously, that translated into high performance across the curriculum. But, our school corporation does not offer accelerated/gifted & talented programs until 3rd grade. Was that a problem for us? No. We have always been educationally minded and did all we could to supplement their education outside the classroom.
I tell you that, not because I want to brag about my girls (I detest that whole look-what-my-kid-can-do trap that so many parents fall into), but only to help emphasize my point. I have always told my girls that everyone's a genius about something, and everyone's a complete idiot about something -- wisdom comes in being able to ascertain where your strengths and weaknesses lie and work with them accordingly. That being said, there's a wealth of learning that takes place in a classroom comprised of students at a variety of academic levels.
Both my girls are quiet and reserved; we chose not to advance them to higher grades because we weren't certain we wanted to have to deal with some of the social issues that would rear their heads once they were approaching high school. The option we chose was to take each of them out of public school after 1st grade. We just completed our sixth year of homeschooling, and have loved every minute of it.
There's so much more to education than test performance and grades, and only you know your child well enough to make these types of decisions. But, having agonized over these same issues in the past, I empathize. Wishing you the best!!
"If we know where we want to go, then even a stony road is bearable." ~~ Horst Koehler