The concepts of cognitive development and objectivity are explored preparatory to a discussion of a suitable theory of development to be used as the foundation for developmentally-based standardized tests. It is hypothesized that Piagetian theory is the most appropriate basis for such tests and two possible approaches for constructing Piagetian-based standardized instruments are presented. It is concluded that since the logical operations approach eliminates two of the three disadvantages of the content conversion approach, it is a more viable means of attacking the problem. A discussion of item construction, scoring and interpretation, validation, and the effects of the use of a Piagetian-based standardized test follow. Examples are given of items in which it is possible to analyze error patterns in order to observe qualitative developmental changes. Emphasis is on the change from concrete to formal operations. Items are derived from Piaget's work by using his scheme of logical operations rather than merely converting the content to a test format. The validity of scores is checked through evaluation of the child's explanation of his responses, the most mature responses exhibiting stable and generalized concept formation. Implications for teacher education and curriculum planning are suggested. (Author/CTM)