This document summarizes the research on test changes to provide an empirical basis for defining accommodations for students with disabilities. It begins by providing an historical overview of special education accountability. It describes how separate special education accountability systems have evolved and summarizes information on the participation of students with disabilities in general education accountability systems. The role of the Individualized Education Program as the main vehicle for expressing the need for test accommodations is emphasized. The paper then summarizes the research on test changes using a taxonomy from the National Center on Educational Outcomes. Testing accommodations are reviewed relating to timing and scheduling of testing, test settings, computer presentation of tests, examiner familiarity, multiple changes in presentation, dictation to a proctor or scribe, using an alternative response, marking responses in test booklets, working collaboratively with other students, using word processors, using calculators, reinforcement, and instruction on test-taking strategies. The last section of the document addresses issues of validity with primary considerations on using this research to implement sound testing practices and to make appropriate educational decisions. (Contains over 170 references.) (CR)