Early studies examining seasonal variation in academic achievement inequality generally concluded that socioeconomic test score gaps grew more over the summer than the school year, suggesting schools served as "equalizers." In this study, we analyze seasonal trends in socioeconomic status (SES) and racial/ethnic test score gaps using nationally representative data from the Early Childhood Longitudinal Study, Kindergarten Class of 2010–2011 (ECLS-K:2011), which includes more school-year and summer rounds than previous national studies. We further examine how inequality dynamics are influenced by the operationalization of inequality. Findings are consistent with a story in which schools initially accelerate relatively lower-achieving groups’ learning more so than higher-achieving groups; however, this school-year equalizing is not consistently maintained and sometimes reverses. When operationalizing inequality as changes in relative position, the reversal of school-year equalizing is more pronounced.