In order to make assessments as widely accessible as possible, including to young learners from diverse backgrounds with a wide range of individual needs and characteristics, some developers of standardized tests have resorted to offering accessibility tools (e.g., magnifying/zoom) and accommodations (e.g., extended response time) to test takers. These solutions have some limitations stemming from the fact that they are retroactively applied to tests. One possible avenue to meet the accessibility needs of diverse students is to proactively address accessibility in the development of test content for all learners. In this article, we report on the development and piloting of a systematic accessibility review process intended for all test content at an organization producing large-scale standardized English proficiency tests for elementary and secondary education students in the United States. We describe the theoretical and research foundations related to fairness, accessibility, and universal design that guided our development of the accessibility review process followed by the process used to develop the tool. The application of the accessibility checklist to a kindergarten English language proficiency assessment is described in detail. Finally, we share some considerations for how the accessibility checklist could be used in other assessment development contexts.