This document opens with a brief discussion of the views of Jean Piaget and his contributions to psychology. The material moves into a presentation of several research studies that have attempted to look at large and representative samples of adolescent pupils, and presents data for comparison in a cross-cultural context. The main sections cover: (1) Background to the Problem; (2) The Mathematical Structure of Formal Thought; (3) The Research Frontier; and (4) The Educational Implications. These sections are followed by five appendices, titled: (1) The Piagetian Journey; (2) The Puzzling Ways of Science; (3) Characteristics of Abstract as Compared to Concrete Thought; (4) Age Ranges for Certain Piagetian Concepts; and (5) The Modification of Concrete Structures into Formal Structures. It is hoped that this material may be useful to research workers and helpful to both teachers and teacher educators. It is felt that the appendices provide sufficient material for beginners to understand the basic Piagetian concepts in an elementary manner. (MP)