Over the past several decades, research has documented strong relationships between social class and children's cognitive abilities. These initial cognitive differences, which are substantial at school entry, increase as children progress through school. Despite the robust findings associated with this research, authors have generally neglected the extent to which school absenteeism exacerbates social class differences in academic development among young children. Using growth-curve analyses within a three-level hierarchical linear modeling framework, this study employs data from the Early Childhood Longitudinal Study (ECLS-K) to examine the links between children's social class, school absences, and academic growth during kindergarten and first grade. Results suggest that the effects of schooling on cognitive development are stronger for lower socioeconomic status (SES) children and that the findings associated with theories of summer learning loss are applicable to literacy development during early elementary school. Indeed, although they continue to achieve at lower absolute levels, socioeconomically disadvantaged children who have good attendance rates gain more literacy skills than their higher SES peers during kindergarten and first grade. (Contains 2 tables, 1 figure and 6 notes.)