The articles in this special issue of the "Journal of Applied Testing Technology" represent significant steps forward in the area of evaluating the validity of methods for assessing the educational achievement of students with disabilities. The studies address some of the most difficult student groups to assess--students with learning disabilities, students with severe cognitive disabilities, deaf/hearing impaired students, students with disabilities who are also English Language Learners, and students who are likely to be inaccurately measured on statewide reading tests. The authors use a variety of research designs and statistical methods to provide evidence for evaluating the validity of assessments of these students. This article highlights the novel contributions of these studies and raises questions for readers to consider as they read each study. (Contains 1 table and 1 footnote.)