I ran across this picture book at the library this week. Those Shoes, by Maribeth Boelts is a wonderful, multiple award-winning book put out by Candlewick Press, a publisher that consistently produces thought-provoking, meaningful books for children.
While Amazon says it's for ages 4-8, I would definitely place it in the elementary-age category. It's one of those that you hope you can get your fourth and fifth grader to read, if they're willing to be seen reading a picture book.
Jeremy is a boy who has noticed that everyone is wearing a particular brand of shoe, but his mother tells him they only have money for needs, not wants. When his shoes fall apart, he is forced to wear embarrassing shoes, and is even more determined to get a pair of those shoes. He finds a too-small pair at a thrift store, and soon discovers the discomfort isn't worth it. He also discovers a classmate with worn out shoes and feet that would fit Jeremy's fancy shoes just fine. While it's hard, he finds giving his shoes to the other boy brings a better kind of joy than fitting in with the crowd. The author brings the lesson home masterfully, without preaching or condescending.
An excellent book for every school-age child, whether fitting in is an issue or not.