The purpose of this paper is to discuss ways in which developmental psychology suffers from the lack of an appropriate technology of measurement and statistical analysis. The paper begins by noting that developmental psychology is the study of change; that individuals develop through a succession of "stages" which are separated by periods of transition. Individual structural theorists differ in their emphasis on the nature, specificity, and discreteness of the stages, and the reversibility of development; but the fundamental notion of structures, their differentiation and integration are common. Problems with assessing developmental variables come about because they are ordinal, and not interval, in nature; the conception of reliability as stability over time is not viable; internal consistency is, likewise, not a sound criterion of reliability; and distributions of developmental assessment are non-normal, and the shape of the distribution would be expected to be different for different age groups. There are also special problems of research design, data collection, and data analysis which research in development poses. To resolve some of these problems, it is suggested that developmental psychologists sit down with measurement people and design ways of analyzing measurement problems, so that measurement and statistics can become a tool to advance developmental theory. (BW)