Within a response to intervention (RTI) framework, students are administered multiple tests of equivalent difficulty. Changes in students' scores over time are then attributed to changes in learning. In the current study, we evaluated the reliability of score changes (i.e., slope) for the easyCBM[R] letter names, word reading fluency, and passage reading fluency measures. Data came from a sample of convenience and included students taking at least three tests of one measure type during one academic year (up to 38 weeks). Data were organized into bi-weekly segments and a growth model for two parallel processes was conducted, with "A" weeks (2A, 3A, 4A, 5A, 6A, 7A, 8A, and 9A) in one process and "B" weeks (2B, 3B, 4B, 5B, 6B, 7B, 8B, and 9B) in the other. A linear growth model was conducted in each process and the individual slopes were estimated within the growth modeling framework. Then, the reliability of the slope was estimated as the correlation between individual slopes from the two parallel processes with a correction by the Spearman-Brown formula. (Contains 15 tables.)