The development of an assessment tool to measure the quality of instruction is necessary to provide an informative accountability system in education. Such a tool should be capable of characterizing the quality of teaching and learning that occurs in actual classrooms, schools, or districts. The purpose of this paper is to describe the development of the Academic Rigor in Mathematics (AR-Math) rubrics of the Instructional Quality Assessment Toolkit and to share the findings from a small pilot study conducted in the Spring of 2003. The study described in this paper examined the instructional quality of mathematics programs in elementary classrooms in two urban school districts. The study assessed the reliability of the AR-Math rubrics, the ability of the AR-Math rubrics to distinguish important difference between districts, the relationships between rubric dimensions, and the generalizability of the assignment collection. Overall, exact reliability ranged from poor to fair, though 1-point reliability was excellent. Even with the small sample size, the rubrics were capable of detecting difference in students' opportunities to learn mathematics in each district. The paper concludes by suggesting how the AR-Math rubrics might serve as professional development tools for mathematics teachers. The following are appended: (1) Score Distributions of AR-Math Lesson Observation Rubrics by District; (2) Score Distributions of AR-Math Assignment Rubrics by District; and (3) 2003 Draft Observation and Assignment Rubrics for Mathematics. (Contains 8 figures and 8 tables.)