A variant of legal evolution theory, based on a model suggested by Turner, is used to explore the determinants of legal differentiation. The most significant study finding is that the reform school organization served as the vehicle and prerequisite for the formal, legal creation of delinquency as a deviant role for children. The second major finding is related to the rate at which reformatories were established in the States. Turner's model, when properly specified, is highly successful in predicting rates of institutional development. Proper specification in this case required inductive analysis of the interrelationships among independent variables and accounting for certain unique historical events. Further insight was gained by examining the functional relationships of independent and dependent variables. Consideration of the ideology of the refuge and reformatory movement has permitted understanding why juvenile law has developed in a manner contrary to the expectations of evolutionary theory. The development of a differentiated legal status for children appears neither as quantitative progress nor as retrogression in the rationalization of law but rather as qualitative change in the value orientation of the rationalization process. The demand for a specialized legal arena for juveniles was raised by nonlegal status groups. These groups were originally of a quasi-theocratic orientation but became increasingly professionalized and scientific as the 19th century progressed. The long-run result of their efforts was a legal order stratified by age and an uneasy partnership of legal and nonlegal professional experts as equal members of the juvenile justice arena. Sixty references, footnotes, tables, and graphs are provided.