The main question the author is trying to answer here is why the USA is so behind on various international knowledge tests for school students. To accomplish this goal, she travels with selected schoolkids to exchange programs in the countries with the highest global testing scores. Unfortunately, the result of the journey isn't comprehensive enough, as Amanda primarily focuses on the individual experiences of the exchange students for most of the book.
Why is Poland better than the States? Who knows — here's a city where the school kid walks around reading classical literature. Why is Korea better than the States? Probably because they study a lot — but behold, they study so much the government had to create studying curfews! Also, students bring pillows to daytime lectures because they study the whole night!
What are the lessons that the author is trying to present? I'm still not sure. Probably the lessons are that the kids must spend more time studying and get frustrated some more. But, again, what about Finland, the author was exploring, yet they have less homework?
Anyway, the book reads more like a fiction novel of youth traveling the world rather than a non-fiction trying to answer a serious question. What makes the smartest kids in the world? I don't know yet, but I'm almost sure it isn't only wandering Polish streets.