It is argued that social media has the potential to bridge formal and informal learning through participatory digital cultures. Exemplars of sophisticated use by young people support this claim, although the majority of young people adopt the role of consumers rather than full participants. Scholars have suggested the potential of social media for integrating formal and informal learning, yet this work is commonly under-theorized. We propose a model theorizing social media as a space for learning with varying attributes of formality and informality. Through two contrasting case studies, we apply our model together with social constructivism and connectivism as theoretical lenses through which to tease out the complexities of learning in various settings. We conclude that our model could reveal new understandings of social media in education, and outline future research directions.