To maintain balance and perform motor tasks successfully, posture must be calibrated relative to a functional spatial reference. Adults efficiently construct movement because of a reliable orientation mechanism attuned to gravity and task constraints. A dearth in data for what young children use as basis (reference) for movement begs the question: What coordinate or orientation system do children use? Children (2-3, 4-6 and 7-9 years; N= 24) and adults (N=11) performed seated bimanual tasks (atop a hydraulic platform) with instructions to maintain upright orientation of a bottle on a tray or held with the hand, under two conditions of trunk motion: 1) subjects voluntarily leaned forward (trunk leading) and, 2) trunk inclination imposed by tilting the support (hydraulic) platform. Specifically, the questions asked were: a) When do children display the ability to keep the balance arm (forearm) oriented to gravity (i.e., horizontal) and, b) What segmental coordination strategies are used at different ages compared to adults? Kinematic data (trunk, arm and forearm positions) were collected and digitized using an optical TV-image processor (E.L.I.T.E. system, Ferrigno & Pedotti, 1985). Segmental displacements were processed, derived (MathWorks Inc.), and used to test for group differences (ANOVA). Segmental strategies, i.e. relationship between trunk and the forearm, predominantly used by each group were analyzed using the correlation between the trunk and the forearm. Comparison of forearm (balancing bottle) displacements revealed that children 2-6 years of age (youngest groups) deviated the most from horizontal in either voluntary (means range from: 11.6 to 25.5 deg) or involuntary conditions (between 4.6 to 5.1 deg; echoes platform inclinations = 5 to 7 deg). Older children, 7-9 years, displayed an emerging ability to constrain forearm displacements (range= 5.3 to 19.1 and 0.6 to 1.9 deg for voluntary and involuntary conditions respectively) while adults uncoupled forearm from trunk motion consistently: displacements were minimized, maintaining a relatively horizontal position with 1.45 to 8 and 0.3 to 1.0 deg displacements (voluntary and involuntary conditions respectively). Young children (2-6 years) used a parsimonious strategy for the dual task (trunk inclination and forearm stabilization): forearm motion was patterned after the initiating segment: support surface and/or the trunk: i.e. egocentric strategy. Similar to the development of other fundamental motor skills (e.g. walking), 7 to 9 years of age appears to be a critical period during which children master postural control and develop an internal representation of body scheme.Keyword(s): early childhood, performance