Background: Less than half of elementary children meet the physical activity recommendations of 30 to 60 minutes of moderate-to-vigorous physical activity (MVPA) on a daily basis. Recess provides the single biggest opportunity for children to accumulate MVPA. This study explored whether a teacher's social prompting to be active during recess alone and modeling of active recess-time games alone may increase the amount of MVPA children accumulate during recess. Methods: Three demographically matched schools were randomly assigned to receive a social prompting intervention, modeling intervention, or to serve as a comparison group. Pre- and postintervention physical activity data was collected utilizing accelerometers. Results: Compared with preintervention, MVPA during recess increased significantly in the social prompting group and decreased significantly in the modeling group. There were no significant changes in the comparison group. There was a significant interaction between time and intervention: pre- to postintervention change between interventions was significant for modeling versus comparison and modeling versus social prompting, but not for social prompting versus comparison. Conclusions: Modeling was not an effective strategy for increasing MVPA during recess. Social prompting may be an effective strategy for increasing MVPA during recess. However, larger studies are needed to determine whether social prompting increases MVPA during recess. In light of evidence suggesting that MVPA is linked to lower obesity rates, and a substantial number of health and academic benefits, social prompting may be a useful strategy to further explore to address the childhood obesity epidemic, and improve students' health and academic outcomes. (Contains 3 tables.)