My perspective is that an ability to work well beyond grade level at this age is a HUGE deal. It's an age where children are less able to tolerate boredom and repetition, and often leads to maladaptive coping measures: acting out on one end of the spectrum, depression and self-harm on the other.

My DD was on the latter end of the spectrum, and we had significant reasons to worry for her mental health if she was to remain in that educational environment... and so she didn't.