Procedures used to map the achievement levels, expressed as total expected scores on the full set of items presented to a grade, onto the Mathematics Composite of the 1990 National Assessment of Educational Progress (NAEP) are described. The Composite, defined as a weighted average of subdomain scores, provides a global measure of mathematics achievement. Levels of basic, advanced, and proficient were set for each of grades 4, 8, and 12 through a consensus process in which a panel of state and local educators, scholars, civic group representatives, and other citizens examined the questions and recommended the proportion that a student needed to answer to reach the defined achievement level. Expected test scores were mapped onto a unidimensional scale with five subscales for grades 8 and 12, and four subscales for grade 4. The process used to map achievement levels directly onto the mathematics composite included: (1) setting empirical item characteristic curves; (2) creating the empirical test characteristic curve; (3) smoothing the overall empirical test characteristic curve; and (4) mapping the cut points onto the composite. Results from the NAEP 1990 assessment had not been released at the time of this paper; thus, numerical results of the mapping are not provided. One table and two graphs illustrate the process. (SLD)