In recent years, increasing numbers of professional development programs have dealt with assessment literacy for teachers and/or administrators. Is assessment literacy merely a fashionable focus for today's professional developers or, in contrast, should it be regarded as a significant area of professional development interest for many years to come? After dividing educators' measurement-related concerns into either classroom assessments or accountability assessments, it is argued that educators' inadequate knowledge in either of these arenas can cripple the quality of education. Assessment literacy is seen, therefore, as a sine qua non for today's competent educator. As such, assessment literacy must be a pivotal content area for current and future staff development endeavors. Thirteen must-understand topics are set forth for consideration by those who design and deliver assessment literacy programs. Until preservice teacher education programs begin producing assessment literate teachers, professional developers must continue to rectify this omission in educators' professional capabilities.