This article introduces the Measurement Skills Assessment (MeSA), which was designed to evaluate the mastery of measurement in elementary school students. The primary objectives for the MeSA include covering a broad range of measurement concepts, distinguishing between major subtypes of measurement, and constructing a continuum of items varying in complexity. This article investigates the psychometric properties of scores from this new test. A series of principal components analyses helps distinguish between two major categories of measurement items--those tapping formula-based/ analytical skills and those tapping spatial/conceptual skills. Rasch analysis provides evidence for the existence of a unidimensional structure of item complexity within each measurement category. The MeSA can be used by psychologists and educators to determine which aspects of measurement present the greatest difficulties for individuals as well as groups of children and to evaluate the effectiveness of different instructional approaches. (Contains 3 tables and 4 figures.)