Learners who experience learning challenges are at risk of not accessing equitable education opportunities in South African schools. This is despite teacher education and system reform initiatives towards more inclusive education. To discover what constrains inclusive teaching, we conducted a qualitative study at four schools in a South African city. At each research site teachers and principals were interviewed and we found teacher, school and system factors implicated in the non-implementation of inclusive teaching practices. In discussing these factors through a Cultural Historical Activity Theory lens, we identify four objects of school activity which are not aligned to inclusive education. These are a competitive ethos, rigid curriculum compliance, bell-curve thinking, and survival in the face of resource limitations. We argue that inclusive teaching will be constrained where it is not aligned with schools' objects-of-activity. To conclude, we suggest strategies that might help to transform objects-of-activity to promote equity and inclusion.