Research on the educational consequences of social media has led to divergent findings that are difficult to integrate and studies often examine specific courses. It remains unclear what types of social media use in classroom prevail on a broader scale and how teachers, if at all, can affect outcomes. We contribute to answering these questions by studying classroom social media use of 459 secondary school teachers in The Netherlands teaching in the humanities, the social, and the natural sciences. We test the idea that the use of social media would be "naturally allied" with self-regulated learning (SRL). Results show that teachers apply social media for information sharing with students outside of the class and, more often, for teaching within the class. A bottleneck consists of the application of social media for the facilitation of SRL. Only in the performance phase of SRL, teachers facilitate SRL via social media slightly. Consequently, the limited use of social media for the facilitation of SRL does not affect student-teacher relationships. Testing the hypothesis of a natural alliance between SRL and social media use, we find evidence for the claim that teachers, who practise SRL in the classroom, are more inclined to use social media.