Federal regulations allow up to 2% of the student population of a state to achieve proficiency for adequate yearly progress by taking an alternate assessment based on modified academic achievement standards (AA-MAS). Such tests are likely to be easier, but as long as a test is considered a valid measure of grade level content, it is allowable as an AA-MAS (U.S. Department of Education, 2007b). In this article, we examine procedures for developing, modifying, and evaluating items and tests using an evolving modification paradigm, as well as a classic reliability and validity framework. Theoretical influences, such as principles of universal design, cognitive load theory, and item development research, are discussed. The Test Accessibility and Modification Inventory, a tool that provides systematic and comprehensive guidance to help educators modify grade-level tests, is introduced. Cognitive lab methods and experimental field tests are then described, along with examples and key findings from each, relevant to AA-MASs. The article concludes with a discussion of precautions, lessons learned, and questions generated about the methods used to improve both access and test score validity for the students who are eligible for this new alternate assessment. (Contains 1 table, 5 figures and 2 footnotes.)