Standardizing accessible test design and development to meet students' individual access needs is a complex task. The following study provides one approach to accessible test design and development using participatory design methods with school community members. Participatory research provides opportunities to empower collaborators by co-creating knowledge that is useful for assessment development. In this study, teachers of students who are visually impaired, students who are blind or are visually impaired, English language teachers, and test administrators provided feedback at critical stages of the development process to explore the construct validity of English language proficiency (ELP) assessments. Students who are blind or visually impaired need to be able to show what they know and can do without impact from construct-irrelevant variance like language acquisition or disability characteristics. Building on our iterative accessible test design, development, and delivery practices, and as part of a large project on English-learner proficiency test accessibility and usability, we collected rich observation and interview data from 17 students who were blind or visually impaired and were enrolled in grades kindergarten through Grade 12. We examined the ratings and item metadata, including assistive technology preferences and interactions, while we used grounded theory approaches to examine qualitative thematic findings. Implications for research and practice are discussed.