I don't have personal experience,
bet I liked this book
http://www.amazon.com/Bright-Kids-Poor-Grades-About/dp/0910707871/ref=sr_1_3?ie=UTF8&s=books&qid=1258614761&sr=1-3 Why Bright Kids Get Poor Grades And What You Can Do About It: A Six-Step Program for Parents and Teachers. Dr. Sylvia Rimm.
"Millions of gifted children are failing to reach their potential something Dr. Sylvia Rimm calls underachievement syndrome."
Here I learned that children need some competition and challenges.
Imagine that you are a runner, olimpic medal winner, and now you have to crawl together with crawlers and to homeworks of this level. how would you feel and what would you do?
Teacher MUST give her another tasks and homeworks which are challenging for her.