With technological development, social networking has become a powerful resource for building relationships, improving collaboration and facilitating learning processes. However, while the majority of educational research on this topic has focused mainly on university students' use of social media, less is known about the potential of social media to enhance social capital and to facilitate learning among adolescents. Thus, the current study examines (1) the nature of relationships between high-school students and their teachers on an online social network and their impact on (2) classroom atmosphere and (3) learning processes. To this end, a Grounded Theory approach was adopted to analyze semi-structured interviews with ten youth aged 15-18 and their teachers and with retrospective follow-up observations of actual online teacher-student interactions. The findings showed that interactions on social media strengthened relationships, improved classroom atmosphere, increased active participation in learning activities, and encouraged collaboration and peer support. However, the findings also shed light why some teachers might avoid communication with students via social networking, although it is imperative to increase their presence in social media for the prevention of online "flaming" behaviors.