It is suffice to say that human being possesses physical, psychological or social defect in that
all human beings are naturally not or not become ‘perfect’. Vygotsky’s study on Defectology
mainly concerns the social characteristic of defect or the complementary activities taken through social development, more specifically the developmental principles of overcompensation, all of which explain the meaning of the previous sentence. According to Vygotsky, all kinds of feebleness and defect should be considered as a source of overcompensation and wherefore the more serious defect is, the bigger the potentiality of overcompensation becomes. Vygotsky’s study has more importance in this sense. The consequences of this study show that disabled children have more complementary potential than non-disabled children do, and those having sever impairment do so more than those having mild impairment do. Hence the researcher of this study would like to suggest that diagnosis be re-considered with this viewpoint of defectology. Also it is hopped that methods of positive diagnosis are to be developed in various ways.