Although mechanical means of measuring physical activity are available, they cannot provide information about the context in which such activity occurs. Therefore, direct-observation systems remain essential tools for studying physical activity. The Observational System for Recording Physical Activity in Children (OSRAC) is a direct-observation system for recording physical activity and associated environmental variables. We evaluated the concurrent validity of the OSRAC physical activity codes with two types of mechanical measures of physical activity: pedometers and heart-rate monitors. The results indicate that heart rates and step totals generally covaried with the OSRAC activity-level codes, suggesting that these codes are valid measures of physical activity in preschool children. Copyright © 2011 John Wiley & Sons, Ltd.