Jean Piaget (1896-1980), renowned Swiss developmental psychologist, is perhaps best known for his groundbreaking epistemological studies with children, which led him to develop a landmark theory of cognitive development. Geldolph A. Kohnstamm's Jean Piaget: Number and Class in Children is a critical study of Piaget's class inclusion theory and its accompanying experiments. The focus is on demonstrating the many attributes of Piagetian argument--theoretical and empirical, logical and psychological. Piaget's inclusion problem experiment was designed to study the development of children's conception of number and class. He placed before them a number of wooden beads, most of which were brown while only two were white. He then asked, -Are there more wooden beads or more brown ones?- Most children younger than eight answered incorrectly, -brown, - illustrating that after acknowledging the parts (color groupings), they simply no longer could see the whole (wooden). Consequently, they took the comparison between part and whole asked for by the question to mean a comparison of the two parts.

In this analytical work, Kohnstamm highlights the connection between the development of number (quantity) and class concepts (relations between groupings within a hierarchy) in children--an idea that had always been of keen interest to Piaget. This work furthers the epistemological conviction, original with Piaget, that number and class develop in close connection with one another in the human mind.