Ethnic minority children living in high poverty neighborhoods are at high risk of having insufficient physical activity (PA) during school days and, thus, the importance of school as a place to facilitate PA in these underserved children has been largely emphasized. This study examined the levels and patterns of PA in minority children, with particular focus on the relative contributions of regular physical education (PE) and school-based afterschool PA program in promoting moderate- and vigorous-intensity PA (MVPA) during school days. PA data were repeatedly measured using a Polar Active accelerometer across multiple school days (M = 5.3 days per child), from seventy-five ethnic minority children attending a Title I public elementary school in a high-poverty neighborhood in the US. The minutes and percentage of MVPA accumulated during school, PE, and afterschool PA program were compared to the current recommendations (≥30-min of MVPA during school hours; and ≥50% of MVPA during PE or afterschool PA program) as well as by the demographic characteristics including sex, grade, ethnicity, and weight status using a general linear mixed model that accounts for repeated observations. On average, children spent 41.6 mins (SE = 1.8) of MVPA during school hours and of those, 14.1 mins (SE = 0.6) were contributed during PE. The average proportion of time spent in MVPA during PE was 31.3% (SE = 1.3), which was significantly lower than the recommendation (≥50% of MVPA), whereas 54.2% (SE = 1.2) of time in afterschool PA program were spent in MVPA. The percentage of monitoring days meeting current recommendations were 69.5% (SE = 0.03), 20.8% (SE = 0.02), and 59.6% (SE = 0.03) for during school, PE, and afterschool PA program, respectively. Our findings highlighted that school-based afterschool PA, in addition to regular PE classes, could be of great benefit to promote PA in minority children during school days. Further research and practice are still needed to increase MVPA during school hours, particularly during PE classes.