Social media platforms and instant messaging applications have a widespread presence in today’s secondary schools. However, the implications of these ubiquitous communication technologies for adolescent’s social functioning with peers and academic competence in the classroom are not well understood. In fact, research on adolescents’ digital lives has only rarely incorporated direct assessments of adjustment in school environments. The current study addressed these limitations with a school-based data collection. 376 adolescents (M_age = 14.4; 209 girls; including 29.2% Latino/Hispanic, 27.3% White, 28.2% mixed) were recruited from an urban high school and followed for one year. Social reputations were indexed via peer nominations and electronic communication tendencies were assessed using self-report questionnaires. Grade point averages, disciplinary events, and attendance data were obtained from school records. On a cross-sectional basis, frequent use of fashionable social networks (i.e., Instagram, Snapchat, and Twitter) was associated with popular-aggressive social reputations, poor achievement, and rule-breaking behavior. E-mail use, in contrast, was associated with academic competence. Longitudinal analyses were less conclusive because the examined constructs were highly stable across the period of data collection. The full pattern of findings indicates that electronic communication patterns can be a powerful marker of academic and social functioning at school.