This article explores how social media use in formal and informal learning spaces can support the development of digital citizenship for secondary school students. As students increasingly spend large amounts of time online (e.g., an average of six hours of screen time per day, excluding school and homework), it is critical that they are developing skills enabling them to find, evaluate, and share information responsibly, engage in constructive conversation with others from diverse backgrounds, and to ensure their online participation is safe, ethical, and legal. And, yet, in spite of the importance of students learning these skills, opportunities for digital citizenship in formal and informal learning spaces have lagged behind our ideals. The article provides a conceptual analysis of civic engagement as digital citizenship and considers how digital media applications can support citizenship education in middle- and high-school grades. Then, empirical research is provided that demonstrates how high school students develop digital citizenship practices through out-of-school practices. Finally, this article suggests that both dimensions of digital citizenship (i.e., in-school, traditional citizenship education and out-of-school activities aimed at civic engagement) can be integrated through a social media-facilitated curriculum. Finally, recommendations for teaching and learning through social media are offered to educators, community members, practitioners, parents, and others.