Posthumanism, or the material turn, refuses to take the distinction between human and nonhuman for granted. Currently discourses in literacy education focus on the ways of incorporating new tools and technologies (products) but within a design perspective, which does not get at the social and participatory ways (processes) of students creating new relationships and realities with materials. A posthuman stance focuses on the processes of literacy artefacts coming into being and what is being produced in the process(es). The social is (re)imagined and (re)defined in processes that encompass social entanglements of humans/nonhuman materials creating newness, new realities. We put to work posthumanist concepts with data that we call the "solar system mural assemblage" from a 7- to 8-year-old Writers' Studio in order to (re)imagine and (re)define social. We question what counts as "social" when working from a posthumanist stance. Why does a "posthumanist social" matter for literacy educators? How does this perspective not only change our research practices but also pedagogies? We wonder how literacies are produced--how realities come into being--in assemblages of human and nonhuman materials in Writers' Studio. We discuss "how" and "why" it matters that we (re)conceptualise the notion of social in literacy education by drawing on posthumanist views.