Background. Childhood overweight and obesity is a serious health issue. Childhood obesity is associated with asthma, hepatic steatosis, sleep apnea, psychosocial complications, increased presence of cardiovascular disease risk factors, and increased medical costs. A decrease in physical activity, an increase in sedentary behavior, and unhealthy eating likely contribute to childhood overweight and obesity. Over the last 3 decades, the prevalence of early childhood obesity has also risen. The level of physical activity that preschoolers engage is influenced by policies and practices of childcare centers they attend. Given the large number of children enrolled in preschool settings and the variability of physical activity among centers, these environments provide a promising opportunity to engage more children in health promoting levels of physical activity. Preschool students are highly sedentary and very little is known about how to significantly increase physical activity in childcare environments with structured, teacher-led activity. Methods. Activity levels among children aged 4-5 in four childcare centers were measured before and after a one-day preschool physical activity teacher training by accelerometry for approximately 5 hours per child over two mornings. Observers coded individual child activities by time. Accelerometer measures of activity levels in METs and related indicators were linked at one-minute intervals with child activity codes. Data were evaluated using single-group repeated measures analysis of variance. Results. After six weeks of implementation the intervention, average MET levels in preschoolers in three of the four centers increased by 11.5% from baseline to follow up. The average MET level per minute for these children at baseline was 2.69±0.40 and at follow-up was 2.98±0.52 (p value= .001). Teachers from all four centers reported spending 24.6 ±13.0 minutes per activity session with up to two sessions completed per day. Teachers reported following the curriculum closely and indicated that the children were generally enthusiastic. Conclusions. These results justify larger trials to determine the impact of physical activity teacher training on the intensity and duration of preschool students' physical activity in childcare settings