In this Monograph, we report the follow-up of 570 adolescents who had been studied as preschoolers in one of two separate investigations of television use. The primary goal of the study was to determine the long-term relations between preschool television viewing and adolescent achievement, behavior, and attitudes. Using a telephone interview and high school transcripts, we assessed adolescent media use; grades in English, science, and math; leisure reading; creativity; aggression; participation in extracurricular activities; use of alcohol and cigarettes; and self-image. In each domain, we tested theories emphasizing the causal role of television content (e.g., social learning, information processing) as contrasted with those theories positing effects of television as a medium, irrespective of content (e.g., time displacement, pacing, interference with language). The results provided much stronger support for content-based hypotheses than for theories emphasizing television as a medium; moreover, the patterns differed for boys and girls. Viewing educational programs as preschoolers was associated with higher grades, reading more books, placing more value on achievement, greater creativity, and less aggression. These associations were more consistent for boys than for girls. By contrast, the girls who were more frequent preschool viewers of violent programs had lower grades than those who were infrequent viewers. These associations held true after taking into account family background, other categories of preschool viewing, and adolescent media use. One hypothesis accounting for the sex differences is that early experiences, such as television viewing, have greater effects when they counteract normative developmental trends and predominant sex-typed socialization influences than when they reinforce them. Adolescents in the study used both television and print media to support ongoing interests. Television content (e.g., entertainment, sports, or world events) predicted extracurricular activities, role models, and body image. The only evidence for possible effects of television as a medium was the positive relation of total viewing to obesity for girls. The medium of television is not homogeneous or monolithic, and content viewed is more important than raw amount. The medium is not the message: The message is.