Significance: Physical activity is important for young persons not only because of its immediate benefits but also because participation in healthy behaviors early in life might lead to healthier lifestyles in adulthood. Persons aged > 2 years should engage in > or = 30 minutes of moderately intense physical activity on all or most days of the week. Walking/bicycling to school provides a convenient opportunity for children to be physically active. To date, only a limited number of reports on this behavior have been made and the results of these reports are variable. This may be due to the exclusive use of subjective methods (i.e., questionnaires) to assess children walking/bicycling to school. Methods are needed in order to provide accurate and consistent descriptions of walking/bicycling to school. The purpose of this study was to develop an objective method for determining the percentage of children walking/bicycling to school. Methods: Two elementary schools with 400-500 students were randomly selected for observation. Trained observers were positioned at three observation points (10 min/observation point) before and after school. The areas observed (observation fields) at each observation point were strictly defined as were the procedures for recording walking/bicycling activity. Results: Over the course of a 3-month period, 30% of the total school days were observed. The average daily prevalence (number of children walking (bicycling) to school/total school population) of children walking to school was 6.6% while only 0.2% biked to school. No gender differences in prevalence rates were observed. Lower prevalence rates were observed on rainy days and on days when the temperature was below 40 degrees F. Prevalence rates were not associated with traffic volume, median home value, or population density. Conclusions: This study provides researchers and educators with an accurate method for assessing walking/bicycling to school behaviors of children. Accurate information of this nature will be important for developing effective programs aimed at increasing walking/bicycling to school and achieving the goals set by Healthy People 2010 concerning children’s trips to school.Keyword(s): measurement/evaluation, physical activity, research