Contrary to Brainerd's (1978) argument that measurement sequences do not provide a useful representation of hypothesized developmental sequences, the basic utility of measurement sequences as indices of age-related changes in cognition is demonstrated. Specifically, a scalable measurement sequence provides ordinal data describing a developmental phenomenon of interest. Because of this basic quality, a theoretically derived and empirically scaled task sequence can be used in robust statistical analyses, such as multiple regression or structural modeling, that enable tests of hypothesized relationships among indices of cognitive development. A scaled sequence of number tasks is presented to illustrate this argument and to test hypotheses concerning the relationship between a Piagetian measure of numerical functional relations and psychometric measures of numerical and perceptual ability. A structural equation model adequately represented the relationships among the four latent variables of age, numerical facility, perceptual speed, and numerical functional relations, demonstrating the utility of measurement sequences as indices of development. Extensions of the proposed procedures are discussed that would provide powerful tests of important theoretical questions regarding more comprehensive representations of developmental processes.