Psychologists and educators have devoted a considerable amount of time to the development of measurement techniques. These have frequently been concerned with the diagnosis of mental and educational dysfunction. This has led to advances in assessment procedures but has also resulted in certain difficulties. Psychology, in particular, has modelled itself on the advanced physical sciences. Psychological and educational measurement techniques, including attempts to minimize error in assessment, have developed to a point where assessment has become separated from the processes of remediation, habilitation and treatment. Psychologists have become preoccupied with building precise techniques of measurement and applied elaborate tools in attempts to measure somewhat elusive factors. This development has been an historically important one, contributing in part to the development of research in the field of education and psychology. However, many of the research findings, particularly in the area which may be loosely defined as special education, have not been applied in the field where there exists a considerable gap between research and practice.