Much is unknown about how initially high-achieving students grow academically, especially given the measurement issues inherent in assessing growth for the highest performing students. This study compared initially high-achieving and average students' growth in reading (in a cohort of third-grade students from 2,000 schools) over 3 years. Using a 3-level longitudinal piecewise hierarchical linear model, we contrasted summer and school year growth rates to examine initially high-achieving and average students' trajectories. Average students grew steeply during the school year and gained nothing over the summer. By contrast, initially high-achieving students grew more slowly than average students during school but maintained that same slower growth rate in the summer.