Professionals with expertise in assessment and diverse learners are in demand to assist in developing and implementing large-scale assessment and accountability systems. This article highlights aspects of current federal legislation that pertain to the development of these systems, describes the areas of expertise and unique perspectives of educational diagnosticians, school psychologists, and special educators that can be used to inform best practice, and emphasizes where additional training is needed to assist educational personnel in taking on new roles. Given the enormous impact that these systems are likely to have on educational agencies, it is argued that individuals with assessment skills and diverse learner expertise must take an active role to ensure the best possible outcomes for all students as these systems are implemented. (Contains 1 table and 2 figures.)