Once I read a good book about underachievement. Now I tried to find it and found this
Underachieving Gifted Child: Recognizing, Understanding, and Reversing Underachievement
http://www.amazon.com/Underachieving-Gifted-Child-Understanding-Underachievement/dp/1593639562 The
There are many other books if you search amazon for keywords "underachievement child".
I was surprised to browse following book tittles
What to Do When Good Enough Isn't Good Enough: The Real Deal on Perfectionism: A Guide for Kids
The Gifted Kids' Survival Guide: For Ages 10 & Under
Bright Minds, Poor Grades: Understanding and Motivating your Underachieving Child
Why Bright Kids Get Poor Grades and What You Can Do about It: A Six-Step Program for Parents and Teachers, 3rd Edition
(this is what I read few years ago; it is about various aspects, mainly in family, that can cause underachievement.)
Social/Emotional Issues, Underachievement, and Counseling of Gifted and Talented Students (Essential Readings in Gifted Education Series)
When Gifted Kids Don't Have All the Answers: How to Meet Their Social and Emotional Needs
Keys to Parenting the Gifted Child
Giftedness, Conflict, and Underachievement
and more.
I wish you a very good luck!