This study examined the reading growth rates of 7,544 students in Grades 2-6, measured over 1 year using Reading-Curriculum-Based Measurement (R-CBM) benchmark assessments administered in the fall, winter, and spring. The authors used hierarchical linear modeling to establish and compare student rates of growth within each grade level based on initial level of performance. Results suggest that growth rates vary significantly, conditional on initial level of performance, with much lower rates of growth for students at the bottom and top of the distribution. Implications for using R-CBM in a response-to-intervention model are discussed. (Contains 3 tables and 5 figures.)