In 2006, a consortium of state departments of education, led by the North Carolina Department of Public Instruction and the Council of Chief State School Officers, was awarded a grant from the U.S. Department of Education to investigate methods of determining comparability of variations of states' assessments used to meet the requirements of the No Child Left Behind Act of 2001 (NCLB). NCLB peer review guidelines includes a requirement that states using variations of their assessments based on grade level academic achievement standards must provide evidence of comparability of proficiency from these variations to proficiency on the general assessment (U.S. Department of Education, July 2007, revised January 2009). The consortium of states focused on two types of K-12 achievement test variations: computer-based tests that are built to mirror the state's paper-based tests and test formats that are designed to be more accessible to specific student populations than the general test is. In addition, the studies conducted included a study of the comparability of an alternate assessment based on modified achievement standards; the comparability issues related to those assessments are different from the ones discussed here. This publication contains the following chapters: (1) Comparability and Test Variations (Phoebe C. Winter); (2) Summary of the Online Comparability Studies for One State's End-of-course Program (Susan M. Lottridge, W. Alan Nicewander, and Howard C. Mitzel); (3) Evaluating the Comparability of English and Spanish Video Accommodations for English Language Learners (Stephen G. Sireci and Craig S. Wells); (4) Evaluating Linguistic Modifications: An Examination of the Comparability of a Plain English Mathematics Assessment (Charles A. DePascale); (5) Evaluating the Comparability of Scores from an Alternative Format (Karen E. Barton and Phoebe C. Winter); (6) Modified Tests for Modified Achievement Standards: Examining the Comparability of Scores to the General Test (Charles A. DePascale); (7) Comparability of Paper-based and Computer-based Tests: A Review of the Methodology (Susan M. Lottridge, W. Alan Nicewander, E. Matthew Schulz, and Howard C. Mitzel); (8) Validity Issues and Empirical Research on Translating Educational Achievement Tests (Stephen G. Sireci); (9) Considerations for Developing and Implementing Translations of Standardized K-12 Assessments (Laura J. Wright); (10) Impact of Language Complexity on the Assessment of ELL Students: A Focus on Linguistic Simplification of Assessment (Jamal Abedi); (11) Alternative Formats: A Review of the Literature (Karen E. Barton and Phoebe C. Winter); and (12) Where Are We and Where Could We Go Next? (Rebecca Kopriva). Individual chapters contain tables, figures and references. (Contains 28 footnotes.) [This report is based on research funded by an Enhanced Assessment Grant from the U.S. Department of Education, awarded to the North Carolina Department of Public Instruction, in partnership with the Council of Chief State School Officers and its SCASS TILSA and SCASS CAS.]