I'm not sure why I finished this book, as I lost interest about 3/4 of the way through. Ironically, it's possible that the reading level was too low for me (I love YA, but this is really more of a middle school read, and that's not my style). That being said, this would be a good book for kids who are struggling with Millicent's problem: being super book smart, but not so bright in the common sense department.
Yee makes Millicent a very believable character. So believable, in fact, that it hurts. Millicent's studying poetry at the college level, but she also thinks her mom has a terminal disease (instead of the very obvious pregnancy symptoms she is manifesting, though possibly not so obvious to a tween). Some story elements verge on the stereotypical: Millicent is horrible at sports, and she's not very nice to people who aren't as smart as she is. That being said, her relationship with her parents was VERY believable, especially with her poor dad, who keeps trying to connect with Millicent over normal kid-type stuff, only to be rejected as childish and silly.
Once we've established that Millicent is book smart and life stupid, Yee introduces Emily, a new girl who befriends Millicent, not knowing she's a genius. Having been burned in the past by people who make fun of her intellect, Millicent pretends to be normal, and actually fools Emily, who is not the sharpest knife in the drawer, but is very kind (and also hurting over her parents' divorce, a subplot element that saves her personality from being extremely annoying).
This is one of those books where people learn lessons, and as such, to an adult audience, it comes over a bit on the didactic side. If, however, you have a gifted child on your hands who needs a few gentle lessons in coping with her/his gifts, this book is a good call. It's also good for the average tween who might be more like Emily than Millicent, and help him/her develop compassion for somebody who can't help the way her/his brain works. I'm a bit too grown up to appreciate it now, but when I was Millicent's age, this book would have been a great comfort to me. Recommended for tween library collections.