Number the Stars uses simple language to tell a complicated story. The heroine, Annemarie, is ten years old, and we get the story mostly through her lens. So fifth graders on up should be able to get through this one with no problems.
But don't forget that Annemarie goes through some crazy tough situations: war, sacrifice, death—none of these are easy topics to stomach. So even though this book is easy to read at the sentence level, the clear, simple words might even mask the danger that the characters face.
All of this makes for a pretty cool effect, we think. Dealing with these subjects through the lens of an innocent young girl really makes us look at this historical period from a different angle.