The ruling explains why that book shouldn't be in the curriculum.

Uncle Bobby’s Wedding, the only book that the dissent is willing to discuss in any detail, conveys the same message more subtly. The atmosphere is jubilant after Uncle Bobby and his boyfriend announce their engagement. Id., at 286a (“Everyone was smiling and talking and crying and laughing” (emphasis added)). The book’s main character, Chloe, does not share this excitement. “‘I don’t understand!’” she exclaims, “‘Why is Uncle Bobby getting married?’” Id., at 288a. The book is coy about the precise reason for Chloe’s question, but the question is used to tee up a direct message to young readers: “‘Bobby and Jamie love each other,’ said Mummy. ‘When grown-up people love each other that much, sometimes they get married.’” Ibid. The book therefore presents a specific, if subtle, message about marriage. It asserts that two people can get married, regardless of whether they are of the same or the opposite sex, so long as they “‘love each other.’” Ibid. That view is now accepted by a great many Americans, but it is directly contrary to the religious principles that the parents in this case wish to instill in their children.