There are lists of traits of gifted kids, and parents are often relieved to find that the "quirks" or behaviors which their kids exhibit, while not typical, are "normal" characteristics among gifted kids.
One example may be a child's dissatisfaction with the classroom arising from correctly observing that s/he is significantly different than his/her classmates in their interests, accumulated knowledge, sense of humor, ability to converse, and/or needing scant exposure to new concepts and information to retain them and make connections.
These kids may be at risk. While some boredom or dissatisfaction with not learning new material in school may be one characteristic common among the gifted, kids will not necessarily exhibit all characteristics, the characteristics they exhibit may change somewhat over time, and no one characteristic is definitive. Gifted kids who do not grow restless with school may be at risk in a different way: risk of "hiding" and underachievement.
Some links which may be of interest -
http://tip.duke.edu/node/99,
http://www.davidsongifted.org/db/Articles_id_10114.aspx
