Ecological Task Analysis (ETA; Davis & Burton, 1991) was employed to examine changes in throwing patterns and perceptual judgments of 4-year old children. ETA incorporates individual and environmental consideration into instructional design for a student-centered approach. It is hypothesized that movement change may emerge from dynamic interaction in given environmental conditions, in the sense that task variability provides opportunities for the performer to choose skills to achieve a task goal as well as a task suitable to his or her capability. The purpose of this study was (1) to identify conditions which either constrain or enhance the development of more mature throwing patterns; and (2) to examine perceptual judgments to task constraints relative to individual physical size (e.g., eye-height level) and capability in throwing. A single case alternating treatment design was used to analyze the data. Targets were created by using hoops (25 inches in diameter) set in vertical, horizontal, and slanting orientations. The target's height was adjusted in relation to the children's eye height level. Each orientation of target was presented at two levels, both lower and higher than eye-height (22 inches and 75 inches from the ground respectively). Four children enrolled in KinderSkills, a preschool motor skill program at a large state university, participated in this study. During the experimental sessions, instruction in throwing skill was restricted. Throwing patterns were categorized in terms of developmental stages to measure variations in throwing. The checklist included the position of the throwing hand and elbow, forearm action, foot position, and stepping in early over-arm throwing (Carson, 1993; Haywood, 1993). Data were collected once a week for a seven-week period and all sessions were videotaped. Inter-observer agreement was assessed. Results found that more mature developmental components were observed in throwing hand and elbow positioning when children attempted to hit high level targets. Homolateral stepping was performed in throwing at both high and low level targets. The subjects jumped and stood on their toes when throwing to a high target instead of stepping. Those actions might produce what the subjects perceived as a more appropriate trajectory relative to the higher target, but they may also hinder the development of more mature throwing patterns. Future research may investigate whether target heights between the two used in this study (slightly higher than eye-height level) may facilitate more advanced throwing patterns. Keyword(s): curriculum, early childhood, motor skills