Sophie is brilliant- stratospherically brilliant. In third grade, she is reading college texts-- her parents are clueless, her teacher is clueless, her classmates uninterested in and uninteresting to Sophie- all fine with her until she realizes that her calculus text is useless without a $100 graphing calculator.
Her classmates are having parent problems of their own and realize a brainiac like Sophie should be able to figure out how to help. Ever logical (a somewhat unappealing) Sophie has no interest in the pedestrian- boring- problems of her classmates until she realizes they will Pay her. Then she is on board, oh until the money falls short, then she is uninterested again.
She is back in the game when she realizes if she helps everyone she will have exactly $100.
All goes as planned until Sophie makes a real sacrifice and ends up with friends instead of $100- who can take that to the bank? Until her friends come through with a new strategy for a calculator.
At the end we still don't know if Sophie has what it takes to be a real girl. The characterizations remain flat and stereotyped to the last page.