The wheel on the school  by Meindert DeJong with illustrations by Maurice Sendak. A classic! also Newbery winner!; not really a back-to-school story, but a story about a school in Holland, and the kids who look for a wheel to put on top, so that storks can make a nest.
Suki's Kimono  by Chieri Uegaki On the first day of school, Suki wears the kimono that her Grandma bought her, even though she knows no one else will be dressed like her.