Just think, Custer graduated 34th in a class of 34 from West Point but went on to be the youngest general in the Union army during the Civil War. Patton did not graduate in the first level of his class at West Point.
What do school grades have to do with innate intellegence?
Each of us have inate tallents that school is not designed to illuminate at their best or even develop. It's only when you are faced with real life do you find out just how good you are at anything. The world is littered with failed geniuses and the average men who worked their butts off and became world leaders, innovators and financial giants in all walks of life.
Geniuses often get bored or are unstable and self destruct.