This paper presents observational and research evidence to refute two widely held beliefs about psychological development: the belief in predetermined development and the belief in the simultaneous development of all behavioral systems. Studies suggesting the plasticity of development through environmental deprivation and intervention are described. Jensen's concept of heritability is challenged with evidence from studies indicating the range of reaction available to children from a wide range of environmental backgrounds. Evidence from studies of orphanage children in Greece and Iran is included in this discussion. Observational and research evidence refuting the belief in global development is also presented. These studies highlight the inadequacy of reliance on the IQ as a measure of overall ability and indicate the value of ordinal scales for measuring achievement in specific areas of development. Evidence for retardation in certain areas of development and concurrent progress in others is said to suggest specific rather than global development. Intervention studies in an orphange in Tehran are described to provide further evidence for asynchronous development. A discussion of the educational implications of these results is included. (BD)