Background: Many children do not meet physical activity (PA) guidelines. One strategy that may enhance PA is to increase active transport to school (ATS) rates. Purpose: To assess the effects of an ATS intervention. Methods: A quasi-experimental design was used to compare ATS and vehicle traffic rates at a school that participated in a statewide event (Nevada Moves Day [NMD]) with those of a control school. Schools were matched on enrollment, ethnicity, socioeconomic status, and neighborhood street patterns. Data collection occurred one week before, on NMD, and one week later. Children using ATS and motor vehicles were counted by university students. Results: Pre-intervention ATS rates were statistically similar at the intervention (10.3%) and control schools (7.8%; P > 0.05). On the NMD, ATS increased to 17.9% at the intervention school and was 7.0% (P < 0.001) at the control school. One week later, ATS rates returned to baseline levels at both schools. The intervention had no effect on motor vehicle traffic. Discussion: A one-day intervention increased ATS rates, but the effect was ephemeral. Translation to Health Education Practice: To institutionalize increases in ATS rates, intervention strategies in addition to a one-day event will likely be required.