For several decades, the Iowa Tests of Basic Skills (ITBS) held the preeminent role in measuring student and school performance in the Chicago Public Schools (CPS), Illinois. In the context of the No Child Left Behind act and new calls for accountability, the CPS has decided to include results from the Illinois Standard Achievement Test (ISAT) in is new system for measuring student performance. The ISAT has been used in Illinois since 1999, but has been overshadowed in Chicago by the ITBS. This data brief compares and contrasts that two tests to bring some needed attention to the ISAT and to assist discussions about the next generation of assessments that must be put into place by the 2005-2006 school year. These tests were created to serve different but not mutually exclusive purposes. The ISAT was developed to measure the extent to which students in Illinois public schools have met the Illinois Learning Standards, which are specific state-defined goals. The ITBS is designed to compare students to a nationally representative group on widely acknowledged basic skills. The brief also compares how these tests are administered, how many questions they contain, and how the questions differ. More complex issues, such as scoring and scaling, are also discussed. Overall, the ISAT "looks and feels" more demanding than the ITBS, in that in both reading and mathematics it is longer and contains more items and extended response items. There is some empirical evidence about correlations between the two tests, and these correlations suggest that students who perform well on one reading test will perform well on the other. The same holds true to a somewhat greater degree for mathematics. Trends for the two sets of tests run mostly parallel. (Contains 4 tables, 9 figures, 41 endnotes, and 12 references.) (SLD)