This study examined whether fine motor skills were related to the initial scores and growth rate of mathematics achievement in American kindergartners and first graders. Participants were 244 East Asian American and 9,816 European American children from the US-based Early Childhood Longitudinal Study (ECLS-K). To control sampling bias, two subsamples of European Americans were matched to the East Asian American sample by socio-economic status or fine motor skills, using propensity score matching. Results showed that East Asian American children possessed more advanced mathematics achievement and fine motor skills. The construct of fine motor skills significantly predicted mathematics achievement over time, and further, it significantly mediated the relationship between ethnic group status and mathematics achievement.