Education is often understood as the sole responsibility of parents and teachers. Reggio Emilia identifies a 3rd teacher between child, teacher, and parent: the environment. In its attention to how space can be thoughtfully arranged, Reggio Emilia has reconceptualized space as a key source of educational provocation and insight. In what ways does this idea support and challenge existing understandings within early childhood education? The article draws on educational literature on space(s) and early childhood education, including but not confined to Reggio Emilia, as well as classroom-based practice, to pursue the implications of the notion of environment as 3rd teacher to classrooms and teacher education and how both preservice and experienced teachers can use this knowledge to inform their practice.