Generations of teachers in trammg have studied aspects of educational psychology as part of their courses. Some have found the subject to be of considerable intellectual interest, but many have felt a degree of frustration at the way a discipline which, on the face of it, ought to have so much to offer teachers, seems to yield few clear cut findings or theories which have obvious and unqualified implications for classroom practice. The study of children's intellectual and social development, of language and thought, of social relationships and personality would seem almost bound to be of direct value to those whose work is, or is to be, teaching. Yet frustration with the lack of apparent utility of what they have learned has been a common outcome for the student.