In an effort to support student agency in assessment, teachers seek to provide detailed instructions and advice in associated assessment task sheets. In this paper, we analyse a sample English assessment task to consider how such assessment design practices might inadvertently create barriers to access and participation. To make our case, we highlight the learning characteristics of students in two of the most prevalent disability groups: students with Attention Deficit Hyperactivity Disorder (ADHD) and students with Developmental Language Disorder (DLD). The paper links student agency to the problem of equity by analysing the conditions and criteria of access that are built into assessment design. The article concludes with design recommendations to help improve access for "all" students, including students in these two highly prevalent disability groups.