The authors used structural equation modeling to map the relationships between student race-ethnicity via the mediating variable physical activity on English language arts (ELA) and mathematics achievement among 964 fourth- and fifth-grade students. The students attended a New York City Metropolitan area school district and completed the Physical Activity Questionnaire for Older Children, which measured weekly average activity levels. Confirmatory factor analysis validated the use of this instrument. Physical activity had a significant, substantive effect on both ELA and mathematics achievement for students, but was most pronounced among White students on ELA and among Black students on mathematics. Hispanic ethnicity had significant direct and indirect negative associations with ELA and mathematics achievement via their decreased physical activity levels relative to White and Black students. These findings help confirm the important link between physical activity and academic achievement and the need to foster more healthy physical activities for students of all races and ethnicities.