overachiever

a person who performs better or achieves more than people are generally expected to, often because of high ambition, pressure from family, etc.: Ever the overachiever, he reached his sales goal for the year a whopping five months early.

a person who performs, especially academically, above the potential indicated by tests of their mental ability or aptitude: We found many overachievers with modest SAT scores who nevertheless achieved high GPAs across a variety of majors.