Background: This study aimed at evaluating the effect of the “Walk,” an 8-month physical activity (PA) program led by classroom and physical education teachers, on the motor competence (MC) and PA of 5- to 6-year-old children. Methods: A total of 143 children (mean age = 61.51 [1.85] mo) participated in the study and were randomly assigned to the experimental and control groups. Children’s MC was assessed by the Körperkoordination Test für Kinder (KTK), and PA was objectively measured by Omron HJ-720IT-E2 pedometers. Measurements were performed at baseline, midintervention, and postintervention. A 1-sample t test computed at baseline step counts revealed that children presented significantly lower PA than recommended for their age (P < .001). To examine the effect of the intervention on children’s MC and PA, several repeated-measures analyses of variance were utilized on (1) KTK item scores and (2) pedometer data. Results: The results revealed that the Walk project led to practically significant changes in the experimental group compared with the control group in both MC (P < .001, η 2 > .14 for all KTK items) and PA (P < .001, η 2 = .23). Conclusions: This study highlights the efficacy of a PA project, involving both classroom and physical education teachers, for the enhancement of children’s MC and PA.