There's A Boy In The Girls' Bathroom by Louis Sachar

A troubled, lonely elementary school boy labeled the worst kid in class lashes out and behaves badly until a patient school counselor sees past his defenses, listens to him, and helps him build self-respect; through her guidance and a tentative friendship with a classmate he begins to change his behavior, confront his fears, and learn responsibility, acceptance, and the possibility of a better life.

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