This book defends that math education should systematically start out from the diverse out-of-school knowledge of children and develop trajectories from there to the Academic Mathematics   tower of knowledge. Learning theories of the sociocultural school (Vygotsky and on) are used here, and ethnographic knowledge from around the world is shown to offer a rich and varied base for curricula. The book takes a political stand against the exclusively western focus  in OECD analyses and proposals on math education.