Social media are widely seen as having transformational potential in school education. However, there is a surprising lack of empirical research in schools about pedagogical designs using social media and particularly the factors that facilitate or hinder desirable outcomes. Consequently, this article offers a review of the limited empirical research literature, and is unique because it not only focuses on school contexts, when the literature is dominated by the tertiary sector, but also because it carefully excludes uses of social media that do not leverage its particular affordances, that is, social interactivity. A synthesis of the literature resulted in a series of design principles for educators, including three broad conclusions that social media for collaborative purposes is best utilised when: (a) social media is not redundant to current practices but offer something new, (b) strategies are in place to help students learn how to work collaboratively, and (c) the tasks are appropriate.