We explored how a progress monitoring and instructional management system can be used to help educators differentiate instruction and meet the wide-ranging learning needs of their increasingly diverse classrooms. We compared classrooms in 24 states that used a curriculum-based progress monitoring and instructional management system, Accelerated Math, to same school control classrooms that did not use it. Among the major findings were the following: (1) At every grade level there were large differences in grade equivalent score and percentile gains for students in the experimental and control classrooms; (2) Gains were experienced across the achievement spectrum. An analysis of low-, middle-, and high-achieving students showed consistent rates of gain for each math objective mastered; (3) Intervention integrity had a significant effect on student achievement; (4) Teachers using the progress monitoring and instructional management system spent more time providing individual versus group instruction and felt better able to meet the individual needs of their students; and (5) Significantly more students who were in classrooms where teachers used the progress monitoring and instructional management system reported that they like math, help each other with math, and like math better this year than last year. Addition of a progress monitoring and instructional management system to ongoing mathematics instruction improves mathematics outcomes for students. The effects of the program clearly are a function of intervention integrity; when progress monitoring and instructional management practices are implemented with high fidelity or integrity, the mathematics performance of all students is significantly enhanced. Implications for practice are discussed.