This article offers composition theorists and practitioners insight into how social media pedagogies can help support the development of distributed expertise in writing classrooms. Reporting on the findings of an IRB-approved qualitative case study, this article showcases how students learning from and alongside one another in a Slack social media learning environment can enact distributed expertise within the classroom. After reviewing the study's findings and contributions, the article offers some "best practices" for supporting distributed expertise with social media pedagogies in composition courses. It closes by considering social justice implications for social media pedagogies, distributed expertise, and composition pedagogy.