The Giver in sixth grade, and I adored it (it remains one of my all-time favorites and started my obsession with all things dystopian/utopian). Later that year, we had to choose an author we'd already read and do a report on another of their books. My aunt had just given me Number the Stars for Christmas when she'd heard how I'd loved The Giver, and so the choice was easy. I loved it then, and I loved just as much this time around.
This story takes a child's perspective on the war and the treatment of Jews. At the same time, there's no "talking down" to the intended audience. It's just a "real" portrayal of the events from a young girls point of view. Lowry nails her level of understanding and misunderstanding, never making her younger than she is or failing to give her credit for her level of maturity.
While much of the events of this book are tame in comparison to what came in later years of the war, I think it's an important story to tell. It's a story of how people risked their lives, even in the face of death, to do what they felt was right. Small or large, every action was a risky one and took courage. I think that's what Lowry conveys in this book. That no matter how insignificant you think your actions are, you can always work to change the things you think need changing.
The diversity of Lowry's work and her ability to write (well) about such a broad range of themese is really interesting to me, and I'd recommend her books to anyone.