The assumption that motor activity and physical manipulation play a central role in early development is evaluated in light of a number of studies reporting that at least some severely physically handicapped children seem to attain age-appropriate or slightly delayed levels of cognitive development. In addition, we examine the importance of motor activity in strong and weak formulations of Piagetian theory, as well as in neo-Piagetian and perceptual analytic [Mandler, 1988] theories. General methodological difficulties affecting interpretation of many studies with the physically handicapped are highlighted. The sufficiency of alternative pathways to development, using available modalities for sensory input and action, is discussed, as well as the possibility of using other people and objects instrumentally to act on the environment in the testing of hypotheses. We conclude that motor activity may be the modal means by which cognitive development normally proceeds, but that it is not a necessary contributor. This view is seen as most consistent with the perceptual analytic and neo-Piagetian models, although neither is specific enough on the issue.