The aim of the article is to explore educational use of student-managed Facebook groups in upper secondary education (in Denmark). Much research on educational potentials of Facebook has studied groups managed by teachers. However, there is a lack of in-depth research on Facebook groups managed by students and without participation from teachers. As this study shows, students' use of student-managed groups differs from their use of teacher-managed tools such as learning management systems (LMSs). The article presents an empirical study based partly on a content analysis of 3139 posts and 15,018 replies within five Facebook groups, and partly on a questionnaire answered by 1463 students and 148 teachers. The results of the study show that whereas LMSs were seen by students primarily as institutional systems of the teacher, Facebook groups have an educational potential to be used by students for peer-to-peer learning.