Our optical and physiological studies of zebrafish reveal that the motor circuits in hindbrain and spinal cord are constructed via an orderly ground plan. Early in life, columns of neurons with similar structure and transcription factor phenotype are arranged by age. Neurons vary systematically in their functional properties and behavioral roles along each age ordered column. Those that differentiate first engage in stronger, faster movements with increasingly younger ones engaged in successively slower and weaker movements. Recent work with a combination of laser perturbation and functional and behavioral studies show how neurons in a column contribute a particular computational role to a network. The picture that emerges from our work is one in which different circuits are built by combinations of a relatively small set of parts, each providing a particular functional contribution to the network. This ground plan is evident both in hindbrain and spinal cord, suggesting that a simple pattern governs the functional development of many different motor networks throughout the nervous system. The plan is later disrupted by migration, which leads to a seemingly much more complicated, messier hindbrain in adults.