Current testing standards call for test developers to provide evidence that testing procedures and test scores, and the inferences made based on the test scores, show evidence of validity and are comparable across subpopulations (American Educational Research Association [AERA], American Psychological Association [APA], & National Council on Measurement in Education [NCME], 1999). Evidence of the comparability of test validity across subpopulations can be collected through examination of: (1) the representation of the content domain being tested; (2) the relationship of test performance to other variables; (3) the internal structure of the test; (4) the response processes of examinees; and (5) the consequences of test score use. This research focuses on examining the internal structure of the test and the response processes of examinees with and without accommodations of test scheduling (e.g., extra time or breaks) and physical setting (private room). In an effort to contribute to the research on the effect of test accommodations on test performance, the current study examines the comparability of academic achievement test performance across examinees who did not receive any test accommodation and examinees who received an accommodation of either (1) extended time only; (2) extended time and private room only; or (3) extended time, private room, and supervised breaks only. These test accommodations represent situations in which there is a change in the scheduling/timing or physical setting of the exam versus the presentation (e.g., audio) or response format (dictated response) of the exam. The equivalence of an academic achievement test's psychometric properties across accommodated and non-accommodated examinees will be examined through the calculation of group descriptive statistics, reliability estimates, standard errors of measurement, and differential item functioning (DIF). (Contains 20 tables.)