wonderful story, beautifully written...with a caveat
This is my all time favorite book. However, the ending for some children can be wrenching. There's no resolution. As adults we know Stuart's "heading in the right direction" but for a child Stuart is heading out alone in the world...his parents left behind, and his beloved Margelo still lost. The aloneness in the world and the searching for something that may never be found can be terribly sad for some children.
My parents read this book aloud to me when I was in preschool, and I was fascinated by Stuart's adventures, which only became more interesting once I read it by myself. All of E.B. White's childrens books are fantastic (especially Trumpet of the Swan), and kids will only wish that the book was longer! Since it is a chapter book with few pictures, it's best read a little at a time with younger kids.
I thought this book was rather disappointing. The review here states that Stuart is valiant and polite and while those are nice characteristics to have, I think that it is overshadowed by his self-pity toward the end. The book kind of falls apart in the last chapters and barely seems to have any continuity. I was trying to justify it by looking for some higher allegorical meaning - but any conclusions that could be drawn seemed to be far too adult for any child of elementary school age to understand or appreciate.