I'm no expert on gifted issues, but I can say my DD9 is like that. We SHOULD have skipped 2nd grade in hindsight. On another forum Suki Wessling had this to say to a similar question about underachievement, and it stuck with me:

Quote
...I think there's a tendency for parents to confuse aptitude with ability and interest. IQ is supposed to test aptitude - basically a test to see how the brain functions on certain tasks. But that has nothing to do with what a child is interested in, what excites him, what drives him. Highly creative people in general are going to be less concerned about academic achievement and more interested in actually *doing* things.

I've also dug up this thread and that thread which touch upon this.

Happy and well-rounded is a great achievement in a gifted child. Many gifted children who are like spearpoints in their focus and passion can have serious emotional and social issues too. When I got DD's test scores back I thought I had failed to recognize some little professor and bought her science books and advanced literature. She showed little interest.

If your child is like my child, I think it's very important they are made to take on a challenge consistently over time, like playing piano. Something where there is infinite room for progress, yet they must work hard to reach the next step, and learn to persevere and break through their perfectionism. Because in 99% of the public schools they are not going to learn that.

For now I'm just making sure DD is truly happy and has opportunities to use her gifts. I also make sure she tells me what's going on inside, because she tends to only adapt and never complain. The other night I was so proud of her. She told me she was being kind to the gifted boy whom the other children tease daily, the one who "knows everything about Harry Potter and snakes" and the one who, when asked in 3rd grade what he wanted most, told the teacher, "for someone to say they love me." She made them stop their teasing game and she has intentionally said hello to him every day since 3rd grade.