Many investigations have been made and much has been written concerning causative factors in juvenile delinquency. Prominent among the causes that have been set forth are low intelligence, emotional instability, psychopathic personality, and poor home and other environmental conditions. Most of the studies have been of a statistical nature with variations in emphasis upon the different factors. Control-group comparisons have been made in a number of instances, but in most cases the degree of control has been inadequate. In numerous cases the delinquents have been compared with groups from the general population, and frequently without regard to age or sex. Data on the control groups have been obtained usually from records already compiled. Differences found between the delinquent and non-delinquent groups have been designated as causative factors in delinquency. Some writers have emphasized the inadequacy of the control-group approach, even at its best, for the diagnosis and treatment of individual cases, although admitting that the data can be used to an advantage in programs for children who present behavior problems. However, it seems to the writer that, if group investigations, adequately controlled, reveal certain factors or traits much more or less prevalent in one group than in the other, these factors or traits might be looked upon as being associated in some way with delinquent behavior. It would seem better, nevertheless, to designate these factors as associated with, rather than causative of, delinquency. It is true some might be designated as causes, either direct or indirect, but others might be more correctly considered as results of delinquent behavior or of the particular circumstances under which delinquents are more frequently found. In this work we shall be interested in discovering whether there are differences in certain abilities, attitudes, interests, and the like, between a delinquent and non-delinquent group, adequately controlled, without emphasizing the causal nature of any differences that might appear. Results obtained from an investigation of this sort might be beneficial in the diagnosis and treatment of delinquency or in indicating the educational and vocational adjustment of the delinquent group so far as any group study could indicate what must be admitted in an individual matter. Nevertheless, these group studies do suggest certain probable satisfactory procedures for the individual case.