The reciprocal fit between the capabilities of a performer and the properties of the environment that permit specific actions to be performed has been termed an "affordance" by James Gibson (1979). Considerable evidence shows that adults are capable of accurately perceiving a variety of affordances for action (e.g., Stoffregen, 2000) and that improvement in the perception of affordances might be one of the fundamental developmental changes across the first two years of life (E. J. Gibson & Pick, 2000). Compared to the attention that has been paid to adults, infants, and toddlers, relatively little attention has been devoted to affordance perception in children above the age of two. The lack of attention is important for at least two reasons: First, accidents are the leading cause of death in children under the age of 18 (Rodriguez & Brown, 1990), inspiring some to suggest that many childhood accidents result from failures in perception and, second, important changes in sensory integration are thought to occur during early childhood (Shumway-Cook & Woollacott, 1985). To further elucidate the perceptual capabilities of young children, the present study compared how children and adults perceived the affordance for upright stance when information was available either visually or haptically. 12 adults (mean age=26.5 years) and 13 children (mean age=4.5 years) examined an adjustable wooden platform that was randomly set at five different degrees of inclination (17, 22, 27, 33, 39). In the haptic condition, a masking curtain excluded vision of the platform and the surface was explored with a hand-held, wooden dowel. Results showed that children overestimated their ability to stand on the steeper slopes, took equal amounts of time to make their judgments across all slopes, and were equally confident in their judgments across all slopes. In contrast, adults were more accurate at judging the affordances for upright stance, took longer to respond close to the actual action boundary, and were less confident close to the action boundary. Furthermore, adults took longer to respond and were less confident in the haptic condition whereas children had similar response times in both conditions and tended to be most confident in the haptic condition. These important differences between adults and children in the perception of a basic affordance are discussed with reference to the coupling between perception and action at different phases of the lifespan and to the role of task constraints in the organization of this coupling.Keyword(s): early childhood, performance, research