This report examines the overlap between student test results on the Iowa Test of Basic Skills (ITBS) and the Washington Assessment of Student Learning (WASL). The two tests were compared and contrasted in terms of content and measurement philosophy, and analyses studied the statistical relationship between the ITBS and the WASL. The ITBS assesses a student's level of achievement within the four broad domains of reading, mathematics, language, and vocabulary. The WASL assesses a student's level of achievement within the four broad domains of reading, mathematics, writing, and listening. The statistical analyses, which considered whether the mathematics and reading subtests of both tests would form two distinct factors or a single underlying factor, were based on individual student-level data for 45,601 students who were given the ITBS in grade 3 in 1999 and grade 4 in 2000. The ITBS and WASL are similar yet different in content and measurement philosophy. In general, students who score high on one test will score high on the other. But the scores on the ITBS and the WASL are not perfectly related, and in some cases, are only weakly related. Results also suggest that the reading and mathematics subtests are more clearly distinguishable on the WASL than on the ITBS. It seems likely that a factor analysis on the individual items would yield a much cleaner distinction between reading and mathematics on both tests. (SLD)