Some states are developing alternate assessments based on modified achievement standards (AA-MAS) to measure the academic achievement of some students with disabilities (Albus, Lazarus, Thurlow, & Cormier, 2009; Lazarus, Thurlow, Christensen, & Cormier, 2007). These assessments measure the same content as the general assessment for a given grade-level, but the AA-MAS may have different expectations of content mastery than the general assessment, according to federal regulations and guidance. The purpose of this paper is to provide a rationale, procedures, and tools to develop and continuously improve AA-MAS ALDs. As states make decisions on whether and how to develop an AA-MAS, they will also be developing a defense of the choices they make. Filben (2008) documented the early peer review process and outcomes and it is clear that choices made must be built on a complex educational logic reflecting content coverage, complexity, and the characteristics of the potential participants. In this paper, the authors propose a process to guide state work so that stakeholders and policymakers can articulate, from the very beginning, the educational rationale for their choices and the implications of this rationale for the specific design choices they make related to their ALDs. By building on this rationale, involving key policymakers and stakeholders through a systematic process to articulate the underlying logic, and documenting how this logic has influenced state choices using the tools and templates provided, states will have compelling evidence for peer review defense. More importantly, they will have confidence in the educational implications of the choices for students and schools in their state. Appendices include: (1) Side-By-Side Tables of Achievement Level Descriptors for Grade-Level and Modified Assessments; (2) Achievement Level Descriptor Analysis Decision Rules; and (3) Procedures and Tools to Evaluate or Develop AA-MAS ALDs. (Contains 28 tables.)