Purpose: Current in-school physical activity (PA) policies lack regulation, which testifies to the urgency of monitoring in-school moderate to vigorous PA (MVPA). This study quantifies the demographical differences of in-school PA among elementary students. Methods: Fourth grade students wore accelerometers during school for 1 week. The teachers logged information for PA setting and duration of opportunity. Results: The accelerometry data (N = 148) showed alarming results in the lack of MVPA during in-school PA opportunity times. Significant sex differences showed boys to accumulate more minutes MVPA per day in recess than girls (7.62 ± 5.87 and 5.19 ± 3.03, respectively). Racial differences showed that non-White students accumulated significantly more minutes of MVPA per week during the school day than White students (30.82 ± 19.09 and 23.44 ± 18.41, respectively). Conclusions: The students fell short of the recommended 30 min of MVPA per day during school hours, as advised by a state mandate. Significant differences were seen in PA levels across sex and race, supporting the need for enhanced attention to influential factors on PA engagement.