Utilizing data on approximately 16,000 children from the Early Childhood Longitudinal Survey-Kindergarten Cohort and a rich set of mediating factors on 16 immigrant groups, this paper examined the associations between children's immigrant generation status and their academic performance. The changes in academic achievements during kindergarten and first-grade were also examined to explore the varying learning paces exhibited by children from different countries of origin. Results indicate that, compared to third and later generation non-Hispanic white children, children of Latin American regions tended to have lower reading and math scores, while children of Asian regions tended to have higher reading and math scores. In addition, although children of immigrants may have either higher (e.g., children from East Asia) or lower scores (e.g., children from Mexico) by first-grade compared to third and later generation non-Hispanic white children, the former generally learned skills at faster paces, thus widening (e.g., for children from East Asia) or narrowing (e.g., for children from Mexico) academic achievement gaps. Child and family characteristics accounted for a large share of the differences in children's academic achievements. Home, school, and neighborhood environments may also matter but to a lesser extent. Research implications are discussed. (Contains 8 tables and 8 footnotes.)