I have personally known guys who were brilliant, 4.0 students from grades 5 through 8. Honor's role in middle school, etc., and then they disappeared in HS and ultimately dropped out. One could argue that while they were clearly intelligent, the lack of resolve and effort which was most likely always there, was bound to lead inevitably to failure, but who knows?
I personally worked hard for my mediocre HS grades. People who wasted tallant and intelligence (at least in certain areas) always pissed me off.