Also a middle school teacher (posting while my students write, actually)! Hey... how many of us are there here, anyway?
So, I really liked this one. I enjoyed the aliens and their - well - alienness. I liked the desperation of the captives, how at first it robbed them of their humanity, but they later fought to regain it. I loved the idea that the aliens didn't mean to be malevolent, but that something about them made it inconceivable to them that the beings they captured were intelligent, like them.
Ok, that's a bit unlikely. If they build cities, make art, and create technology they're probably intelligent. Still, it's a neat possibility.
I also liked the ambiguously "happy" ending. I agree with StepH. They're probably not getting out of their alive, especially Kid, who is moments from bleeding to death. Still, sometimes a symbolic victory is the best you can do. Sometimes that's enough. And who knows? Maybe they will make it.