Current research concerned with the role of experience in development is directed to assessing the effects of training on child behavior. This approach is discussed as a general strategy for experimental research in the study of developmental phenomena, and for its implications in contrasting models of development in terms of their assumptions relating to the joint roles of experience and maturation in behavior. The similarities of these assumptions to those made in learning theories are also discussed. In addition, experimental methods for the systematic assessment of training-related changes in behavior are presented as procedures for studying phenomena which typically covary with age in the natural environment.