Many schools are implementing multitier response-to-intervention (RTI) models to reduce reading difficulties. This study was part of our larger ongoing longitudinal RTI investigation within the Florida Learning Disabilities Center grant and was conducted in 7 ethnically and socioeconomically diverse schools. We observed reading instruction in 20 classrooms, examined response rates to kindergarten Tier 1 instruction, and predicted students' first-grade reading performance based on kindergarten growth and end-of-year reading performance (n = 203). Teachers followed an explicit core reading program. Overall, classroom instruction was rated as effective. Results indicate that controlling for students' end-of-kindergarten reading, their growth across kindergarten on a variety of language and literacy measures suppressed predictions of first-grade performance. Specifically, the steeper the students' trajectory to a satisfactory outcome, the less likely they were to demonstrate good performance in first grade. Implications for future research and RTI implementation are discussed. (Contains 4 tables.)