Background: We compared moderate-to-vigorous intensity physical activity (MVPA) and inactivity levels among fifth and sixth graders during school hours according to school-level race/ethnicity and income attributes to inform school-based obesity interventions in Illinois Suburban Cook County (SCC). Methods: Fifth- and sixth-grade students (N?=?591) in 14 SCC public schools were asked to wear an accelerometer during school hours for 4 consecutive school days. School-level race/ethnicity was assigned based on the majority (=70%) race/ethnicity of the student population: white (N?=?4), black (N?=?2), Hispanic (N?=?5), or "mixed" (N?=?3). All minority schools (N?=?7) fell within a low-income category. Results: A total of 538 students (91%) had valid accelerometry data. Average MVPA time during school hours was 20?minutes/day for boys and 11 minutes/day for girls. Multilevel linear regression models showed that compared to peers in white schools, boys, and girls in Hispanic schools engaged in 14 and 10?minutes less MVPA, respectively (p?<?0.01). Girls in black and Hispanic schools had greater inactivity time than girls in white schools (p?<?0.01). Conclusions: Objectively measured physical activity (PA) data support the need for school-level PA interventions during school hours, particularly in predominantly Hispanic schools.