Little is known about the academic impact of social media and addictive phone use among U.S. adolescents. This study examined the specific impact of school-time social media use, and addictive phone use, on adolescent’s academic performance. The study cohort initially consisted of 918 adolescents (92% White) who completed an assessment process (based on self-reported data) of their social media use, addictive phone use, and academic performance. Eliminating those who had no smartphone reduced the number of subjects by almost a third (to 641). Statistical analyses of the subjects’ self-reported assessment data indicated that the amount of time they spent using social media during the school day predicted poor academic performance, and that addictive phone use further predicted poorer academic performance. School administrators should address school-time social media use and addictive phone use to enhance their students’ academic performance.