In her high school days, she blended in with the other students in the school. If a person didn't know who she was, they would have walked by her without so much as a polite hello.
She was on the track team along with another notable, Sue Bird, who is one of the WNBA all-time greats. When the team handed out the awards at the end of the season, Natalie was recognized as having one the top grade point averages in her senior class.
Up close and personal she is reserved and focused on the task at hand. If intelligence is measured by problem-solving ability, then yes, Natalie ranks very high. But intelligence can be measured in many different ways: academically, emotionally, psychologically, artistically, etc.
Natalie Portman doesn't seek to impress people with her academic record or acting ability. Even if she wasn't in high-profile world of entertainment, she would simply give her best effort to the task at hand.