Piaget's theories of the structure of knowledge, constructivist learning, and stages of development in thinking have been a cornerstone of cognitive psychology and teacher education for half a century (Piaget, 1983). More recently, his ideas about stages of cognitive development have received criticism from many quarters (Weiten, 1992), including from neurological research. In Piaget's defense, in common with all theories, his are a product of their time based upon the evidence available. This article shows that Piaget is not wrong, and that when Piaget's ideas are reviewed with reference to new evidence from brain research one can see that some of his basic principles are still relevant to teaching today. His constructivist views fit very neatly with the undeniable flexibility of the brain to respond and grow as the result of experience. Although Piaget's ideas about stages of development have been challenged with new evidence, the three studies discussed in this article show clearly that there are periods of optimal performance and spurts of growth, and that these are in agreement.