From the Arizona Department of Education website:
The Accountability Section aims to measure the growth in quality of Arizona schools and districts by producing timely and reliable accountability determinations as required by state and federal law. The section works closely with Assessments, the State Board of Education, and Research & Evaluation in order to accurately label schools in a fair and systematic manner. Accountability staff support schools, districts, and other stakeholders to refine the system as well as utilize data in an appropriate and effective manner.
For more information on these labels and grades you may view the MPS video here. (http://www.edtv99.org/video/9740/)