Given the need to find more opportunities for physical activity (PA) within the elementary school day, this study was designed to asses the effect of Initiatives for Children's Activity and Nutrition (I-CAN!) active lessons on the following: 1) student PA outcomes via accelerometry and 2) socioeconomic status (SES), race, sex, body mass index (BMI), or fitness as moderators of this effect. Participants were 2493 fourth-grade students (45.9% male, 45.8% white, 21.7% low SES) from 28 central Texas elementary schools randomly assigned to intervention (n = 19) or control (n = 9). Multilevel regression models evaluated the effect of I-CAN! on PA, and effect sizes were calculated. The moderating effects of SES, race, sex, BMI, and fitness were examined in separate models. Students in treatment schools took significantly more steps than did those in control schools (β = 125.267, SE = 41.327, P = 0.002, d = 0.44). I-CAN! had a significant effect on moderate- to vigorous-intensity PA (MVPA), with treatment schools realizing 80% (β = 0.796, SE = 0.251, P = 0.001, d = 0.38) more MVPA than the control schools. There were no significant school-level differences on sedentary behavior (β = −0.177, SE = 0.824, P = 0.83). SES, race, sex, BMI, and fitness level did not moderate the effect of active learning on step count and MVPA. In conclusion, active learning increases PA within elementary students, and does so consistently across demographic subgroups. This is important because these subgroups represent harder-to-reach populations for PA interventions. Although these lessons may not be enough to help children reach daily recommendations of PA, they can supplement other opportunities for PA. This speaks to the potential of schools to adopt policy change to require active learning.