Information literacy, ie the competent dealing with information, is considered a key competence for the networked information and media society that facilitates civic engagement, a self-determined life, and lifelong learning. With the rise of social media, many new information sources have emerged, opening up new challenges. Despite their growing importance, little is known in information systems research and education about information literacy in the context of social media. Against this background, we propose and empirically test a framework for modelling and measuring social media literacy (SML) in secondary school. Applying the proposed framework on a survey with 434 high school pupils from Germany, Austria, Switzerland, and Liechtenstein, we find relatively poor skill levels in the objective SML for most students, while the self-assessed SML is slightly higher. In addition, the study reveals that three different forms of social media use can explain individual differences in SML.