Jean Piaget, renowned Swiss developmental psychologist and epistemologist, is best known for his groundbreaking studies with children, which led him to develop a landmark theory of cognitive development. Geldolph A. Kohnstamm’s Jean Piaget: Children and the Inclusion Problem is a critical study of a cornerstone of Piaget’s theory. This theory holds that a child’s ability to solve problems of class inclusion marks the beginning of the period of concrete (logical) operations at about seven or eight years of age.Kohnstamm’s experiments show, however, that with directive teaching methods, most children of five can already learn to solve inclusion problems. His results make him question the basic assumption of Piaget’s theory that logical operations can only develop in firmly connected groupings of operations, not in isolation. The author argues that experimenters must therefore show that children who come to master one kind of operation should also show transference to other operations of the same grouping. As a result, he questions the real existence in brain functioning of the hypothesized groupings of operations in Piaget’s theory.This book is a revised edition of the 1967 original and includes a new introduction and epilogue. The original book was published in the Netherlands, not in the United States. Therefore it has reached only a negligible US audience and has sadly escaped the attention of many interested in Piaget’s developmental theory. This challenge to Piaget’s theory is an invaluable resource for cognitive, developmental, and educational psychologists.