Citizens turn increasingly to social media to get their political information. However, it is currently unclear whether using these platforms actually makes them more politically knowledgeable. While some researchers claim that social media play a critical role in the learning of political information within the modern media environment, others posit that the great potential for learning about politics on social media is rarely fulfilled. The current study tests which of these conflicting theoretical claims is supported by the existing empirical literature. A preregistered meta-analysis of 76 studies (N=442,136) reveals no evidence of any political learning on social media in observational studies, and statistically significant but substantively small increases in knowledge in experiments. These small-to-nonexistent knowledge gains are observed across social media platforms, types of knowledge, countries, and periods. Our findings suggest that the contribution of social media toward a more politically informed citizenry is minimal.