Taking culpabiity away from the kid, and looking for what is missing, I believe the answer is metacognition.
In most school and education programs, there is such a content focus that there is an assumption that secondary skills will just automatically accrete through negative feedback.
I think many gifted kids need direct and formal learning related to metacognitive skills. When they automatically know how to solve a puzzle, add, understand words in context, the slowed down plodding path to solution rarely or never happens. When faced with questions of "show your work" or "how did you arrive at this", etc. they don't actually have the answers.
Here is a good backgrounder on it:
http://www.nagc.org/index.aspx?id=205
