The two don't correlate. And I say that while working on two Master's degrees. Academia is a very specific format of teaching and testing and politics (yes, even at the student level: ever had to write about a topic you're not interested in as though it was FASCINATING?). I've worked with Mensa members who barely graduated high school. You can be smart and good at school or smart and bad at school, but the ability to fit yourself into the student paradigm is no indicator of intelligence.

Also, once you do well or poorly in school, the label becomes systemic and that determines future scholastic expectations and opportunities. The system has a lot of problems, as well as merits.