I read this book along with my tutoring student: it was her going-in-to-10th-grade summer reading assignment. I'll try to include both our perspectives, as she's certainly much closer to the intended audience than I am.
I tell you what, though: I'm surprised by the school's choice. These students are 14/15 years old, but the book's protagonists, Tyler and Mari, are only 11. I don't believe that the old "kids only want to read about older kids" saw is universally true (of the millions of 9th graders annually subjected to To Kill a Mockingbird, I'm sure a substantial number get quite attached to Scout and Jem), but for my particular student, it didn't help that Tyler in particular acts quite young. Or as she kept putting it, "he's such a goody two-shoes!"
Actually, there is a striking difference in how the two characters resonated with us. To my mind, Tyler seems like he would have fit better in a children's book from the 1950's, while we found Mari to be refreshingly relatable. To illustrate:
Tyler loves: astronomy, helping out around his family farm, and America. Problems: his dad's been injured, the farm's in trouble, and if anyone catches the illegal migrant workers they're employing, it could put them out of business.
Mari loves: writing letters, listening to her uncle's songs and jokes, and (after meeting Tyler), astronomy. Problems: her mom's been missing for nearly a year now, her family lives in constant danger of discovery and deportation, and she has the frustrating job of looking after her younger sisters.
I was surprised by how readily my student gravitated towards Mari, and asked her why she thought Mari was so much more interesting as a character. I think her exact words were, "Well, Mari's got real stuff to deal with, you know. She misses her mom, and the kids at school are mean to her, and she has to take care of her sisters, even though there's nobody really to take care of her. Tyler's just a bunch of first-world problems."
(NB: This transcription may be missing hashtags)
Setting aside the two narrators, we both enjoyed the actual plot pretty well. It moves along at a good clip, with incidents both big and small, and a surprisingly realistic and satisfying conclusion. Our only major gripe (and it's one we both noticed) is that Ms. Alvarez's decision to render Mari's PoV entirely through letter-writing exercises was often forced and artificial. For example, here she is writing a letter to her uncle, describing the trial he himself has just participated in:
"You seemed unsure why the judge wanted to know such personal information. But you shook your head and explained that you had been working since you were a boy helping your parents and six sisters and brothers. You hadn't had any time to court a girl, much less marry one and have kids."
If there is a reason why Mari needs to summarize and repeat her uncle's own experience back to him, it's not made clear in the text. Again, not a fatal flaw, but given that Mari's sections are roughly half the book, an unfortunate one.
Actually, there is a bit of that artificiality that seems to bleed through the whole novel. It's pretty clear that this story was built for the express purpose of criticizing American immigration policy and highlighting its impact on real families and communities, and it does that very effectively. The children are heart-tuggingly earnest and sincere, their families are loving and flawed (but only in the most heart-tuggingly attractive ways), and even curmudgeonly Old Man Withers is eventually brought around to the cause of justice with the help of a few Mexican-American cherubs and some of granny's apple pie. It's very neat work.
But there is a reason Captain Planet isn't as successful as Superman, and I think ultimately our lukewarm response to this book stems from the same effect. It's all right to include lessons and morals in the story – a little fictional fiber is good for all of us. But when you feel like every part of the story is custom-designed to showcase a Very Important Issue, the characters start to look less like people and more like puppets – and you the reader start to feel less like a person to be entertained and more like a student to be taught. For one of us, of course, that's indisputably true, but she didn't especially appreciate the reminder.