Despite decades of tenacious advocacy and improvement efforts to expand and enshrine rights for students with disabilities, many students with individualized education programs (IEPs) still lack access to high-quality, effective learning opportunities. This can be due to a range of factors, including low expectations, exclusion from general education classrooms and curricula, or learning experiences that are poorly designed to meet their needs. As a result, education outcomes (including academic achievement and graduation rates) for students with disabilities lag behind those of their peers. This brief focuses on a promising approach to addressing and overcoming these enduring inequitable outcomes: implementing an inclusive, coherent, and effective assessment system. In fact, an assessment system designed with the principles of inclusion and coherence and focused on effectively supporting the learning of students with disabilities in mind can benefit all students through recognition of learner variability. Such an assessment system is integral to any effort to improve education opportunities and outcomes, given that assessment is the fundamental way educators, administrators, and policymakers understand and respond to evidence of student learning.