Using the first 4 waves of data from the Early Childhood Longitudinal Study-Kindergarten cohort (ECLS-K), this piecewise 3-level (time-student-school) growth-curve model provides a portrait of students' reading growth over the first 2 years of school. On average, students make much greater reading gains in 1st grade than they do in kindergarten. First-grade monthly reading growth averages 2.65 points per month, whereas kindergarteners make approximately 1.67 points of reading growth per month. Student-level variables (including socioeconomic status, ethnicity, kindergarten entry age, and gender) were better able to explain between-schools variability in students' initial reading scores and students' reading growth than school-level variables (percentage of minority students, percentage of free-lunch students, and sector). Although socioeconomic status had a minimal impact on reading growth while school was in session, it had a larger impact on summer reading growth. These results suggest that between-schools differences in achievement are largely explained by the differences in school clientele, rather than differences in instruction or resource allocation. These results also underscore the potential importance of preschool and summer programs for low-socioeconomic status children.