"High Schools That Work" (HSTW) is a school improvement initiative that was inaugurated by the Southern Regional Education Board (SREB) in 1987. The main purpose of this concurrent validity study is to evaluate one or more measures by investigating their relationship to other commonly used and established measures given at or about the same time to a group of individuals. The results from these analyses provide strong empirical support for the concurrent validity of the new "HSTW" Assessment, given for the first time in 2008. The results showed that the scores from the "HSTW" Assessment are generally moderately to highly correlated with all of the other measures of student achievement, and that the correlations fit an expected pattern since the "HSTW" Assessment scores correlated more highly with state test scores in the same content area than with state test scores in a different content area or with high school GPA. In addition, all of the correlations between the "HSTW" Assessment scores and the corresponding section scores from both of the national college admissions tests are substantial, which appears to indicate that low student motivation was not an issue for the "HSTW" Assessment, at least for the subset of students in this study who also took the ACT or SAT. (Contains 5 tables.)