The papers in this volume relate to the nature and conditions of classroom learning, with particular emphasis on the cognitive aspects. They are concerned with the question of concept formation and stress the importance of the teacher’s function in ensuring that the child really has assimilated the ideas and not merely the words for the concepts. The role of language is fundamental to this theme, and the interaction of language, thinking and learning is dealt with in the first section of the book. This section also provides a context within which subsequent discussions of classroom learning problems can be viewed. Some problems concerning the elaboration of a general theory of teaching are then examined with particular reference to possible methods of bridging the gap between research and implementation.