The art of teaching is based primarily upon the science of psychology. In this book the authors have sought to make clear the principles of psychology which are involved in teaching, and to show definitely their application in the work of the classroom. The book has been written in language as free from technical terms as is possible. In a discussion of the methods of teaching it is necessary to consider the ends or aims involved, as well as the process. The authors have, on this account, included a chapter on the work of the teacher, in which is discussed the aims of education. The success or failure of the work of a teacher is determined by the changes which are brought to pass in the children who are being taught. This book, therefore, includes a chapter on the measurement of the achievements of children. Throughout the book the discussion of the art of teaching is always modified by an acceptance upon the part of the writers of the social purpose of education. The treatment of each topic will be found to be based -upon investigations and researches in the fields of psychology and education which involve the measurement of the achievements of children and of adults under varying conditions. Wherever possible, the relation between the principle of teaching laid down and the scientific inquiry upon which it is based is indicated.