Objective: This study examines effects of a school garden intervention on elementary school children's physical activity (PA). Method: Twelve schools in New York were randomly assigned to receive the school garden intervention (n = 6) or to the waitlist control group that later received gardens (n = 6). PA was measured by self-report survey (Girls Health Enrichment Multi-site Study Activity Questionnaire) (N = 227) and accelerometry (N = 124,8 schools) at baseline (Fall 2011) and follow-up (Spring 2012, Fall 2012, Spring 2013). Direct observation (N = 117,4 schools) was employed to compare indoor (classroom) and outdoor (garden) PA. Analysis was by general linear mixed models. Results: Survey data indicate garden intervention children's reports of usual sedentary activity decreased from pre-garden baseline to post-garden more than the control group children's (Delta = -.19, p = .001). Accelerometry data reveal that during the school day, children in the garden intervention showed a greater increase in percent of time spent in moderate and moderate-to-vigorous PA from baseline to follow-up than the control group children (Delta = +.58, p = .010; Delta = +1.0, p = .044). Direct observation within-group comparison of children at schools with gardens revealed that children move more and sit less during an outdoor garden-based lesson than during an indoor, classroom-based lesson. Conclusion: School gardens show some promise to promote children's PA. (C) 2014 Elsevier Inc. All rights reserved.