"between 10 percent and 20 percent of high school dropouts are intellectually gifted, and 40 percent of those who graduate in the top 5 percent of their high school class do not complete college."
The OASIS Guide to Asperger Syndrome by Patricia Romanowski Bashe and Barbara L. Kirby
(see links in sidebar for more info on Asperger's)
At the very least, I think this indicates that a. it's not only students with low IQ or who struggle in school that need encouragement and emotional support and b. many schools are failing the above average students as well as those who don't fit in because of academic weaknesses. It is hypothesized in this book that learning disabilities such as Asperger's and ADHD might help account for these surprising statistics, particularly since these conditions are less likely to be diagnosed in gifted students.
(by the way, gifted is considered an IQ of 130 or above)