Test accommodations are often given to students with disabilities as one means of removing construct-irrelevant barriers to proper measurement of their knowledge, skills, and abilities. However, the practice is controversial. This article reviews numerous studies that focused on the effects of accommodations on test performance. Consistent conclusions were not found across studies because of the wide variety of accommodations, the various ways in which they were implemented, and the heterogeneity of students to whom they were given. But two consistent findings emerged: Extended time tended to improve the performance of all students, although students with disabilities tended to exhibit relatively greater score gains; and oral accommodations on math tests were associated with increased test performance for some students with disabilities. (Contains 4 footnotes, 5 tables and 2 figures.)