[In Up in Seth's Room, fifteen year old Finn] feels confident that she wants to remain a virgin despite pressure to "go all the way"…. [It] is not until Finn meets handsome Seth … that her attitude is put to the test. Ignoring prohibitions from her disapproving family …, Finn begins to see Seth in secret and the two develop real feelings for each other. Their sexual relationship is limited to kissing and petting until Seth finds his own apartment when matters rapidly change. After an encounter that stops just short of force, the pair realizes that Seth has interpreted Finn's resistance as a challenge to his masculinity. The knowledge affects them both, forcing Finn to weigh her romantic attachment to Seth with her right to govern her own desires and helping Seth reevaluate his ideas about relationships between men and women. While sexual encounters are explicit, Mazer focuses on the emotions they engender rather than the acts themselves, and an obvious message to teenagers is softened considerably by the use of natural dialogue and well-rounded characters.
A review of "Up in Seth's Room," in Booklist (reprinted by permission of the American Library Association; copyright © 1979 by the American Library Association), Vol. 76, No. 5, November 1, 1979, p. 440.