The U.S. federal Every Student Succeeds Act (ESSA) was enacted with goals of closing achievement gaps and providing all students with access to equitable and high-quality instruction. One requirement of ESSA is annual statewide testing of students in grades 3-8 and once in high school. Some students, including many deaf or hard-of-hearing (D/HH) students, are eligible to use test supports, in the form of accommodations and accessibility tools, during state testing. Although technology allows accommodations and accessibility tools to be embedded within a digital assessment system, the success of this approach depends on the ability of test developers to appropriately represent content in accommodated forms. The Guidelines for Accessible Assessment Project (GAAP) sought to develop evidence- and consensus-based guidelines for representing test content in American Sign Language. In this article, we present an overview of GAAP, review of the literature, rationale, qualitative and quantitative research findings, and lessons learned.