Klass’s writing career began with the novel "The Atami Dragons", inspired by his experiences as an English teacher in Japan. His 1994 book "California Blue" gathered very positive reviews for its quiet yet compelling treatment of environmental issues. In 2001 Klass published "You don’t know me", which uses an edgy first-person narrative to tell the story of a teenage boy’s life with an abusive stepfather-to-be. The book has been published in 18 languages, was named an ALA Best Book For Young Adults, and continues to be popular with young adult audiences in the United States and internationally.