In current discourses, learning and development are rarely distinguished even though Vygotsky critiqued psychology for not distinguishing quantitative (learning) from qualitative (development) change. To him, the two are distinct but related processes. Their connection is conceptualized in the law of the transition of quantity into quality. Learning is slow, cumulative (quantitative) change that occurs as we become better at doing whatever we do in practice. Development, on the other hand, is a qualitative change in which existing ways of doing, speaking, and understanding are overturned, leading to very different forms of experience. In chapter 6, we articulate a way out of the old dilemma where change of thinking is modeled either in terms of discontinuities (à la Piaget) or in terms of continuity (maturation). Using a classical problem in educational and developmental psychology, reasoning on the balance beam, we show with empirical materials how learning and development can be articulated (connected) in a dialectical approach characterized by the law of the transformation of quantity into quality and quality into quantity