The “psychological turn” taken during the 20th century seemed to be a major advance. It promised an objective way to make the triangular fix between development, mathematics and education. Using Toulmin's (1953) analogy, what seemed to be on offer was an accurate map of learning along with a good itinerary through education. This promise turned out to be hard to keep, not merely in the particular case of mathematics learning, but quite generally in psychology-inspired work on the classroom. After 100 years of systematic research in education and educational psychology, there is still no agreement about whether, how, or under what conditions research can improve educational practice (Weinert, & de Corte (1996) F. Weinert and E. de Corte, Translating research into practice In: E. de Corte and F. Weinert, Editors, International encyclopaedia of developmental and instructional psychology, Pergamon, Oxford (1996).Weinert & de Corte, 1996).