The sequence of development as hypothesized by Piaget has been confirmed for various groups of children by cross-sectional and longitudinal studies. Such consistency has increased interest in constructing scales based on Piaget's theory according to psychometric principles. Three major problems are discussed which present definite obstacles in the development of a general scale: (1) A Piagetian test, encompassing all stages and operations within individual states, would be so broad in scope that thorough testing may be precluded; (2) Piaget's clinical method of questioning may not be amenable to standardization, resulting in unreliability from a psychometric standpoint; and (3) Piagetian demonstrations have been presented in many different forms and at various degrees of complexity; such diversity necessitates an imposing task of selecting a set of items most representative of the sequency of development. Considering these overriding problems, it is concluded that one scale representing Piagetian development in general may be an impossibility. (Author/KM)