This perspective paper reviews the linkage between developing postural control and upper extremity function. We suggest updated principles for guiding clinical practice, based on current views from motor learning, motor development, and motor control research. Using three clinical examples, we illustrate principles focusing on the use of variability, the importance of errors in learning movement, task specific exploration and practice, and the critical timing necessary to build skill of the upper extremity in a variety of postures. These principles differ from historic approaches in therapeutic exercise, which treated posture as a separate system and a precursor for extremity skill building. We maintain that current movement science supports the tight interaction of posture and upper extremity function through developmental time and in real time, such that one system cannot be considered separate from the other. Specific suggestions for clinical practice flow from the guiding principles outlined in this paper.