If success in school is a function of intelligence and hard work, and less intelligent students have to work harder to achieve the same grades as their more intelligent counterparts, only hard work seems to matter in predicting career success.
Sadly, it's also an idea that is going out of style in a society where students expect to get good grades just for showing up, where everyone gets a ribbon no matter where they finish, and where parents scheme to get their kids into college by lobbying state legislatures to create set-asides for in-state residents at public universities.