High stakes test-based accountability systems primarily rely on aggregates and derivatives of scores from tests that were originally developed to measure individual student mastery of content specifications. Current validity models do not explicitly address this use of aggregate scores to measure the performance of teachers, administrators, and schools. Empirical methodologies that allow evaluation of test-based accountability systems need to be identified and developed. One empirical method that lends itself to the comparison of individual and group-level outcomes is hierarchical generalized linear modeling (HGLM). This research explores the validation of aggregate scores used in accountability. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]