The tables of a few hundred juvenile delinquents and school children examined in Minneapolis, which are presented in this book, indicate the occasion rather than the aim of the present study. The purpose is mainly to help clear the ground for other work with mental tests, and especially to put the determination of feeble-mindedness by objective examination with the Binet or other scales on what seems to me a sounder basis. Furthermore, the results of objective testing which have been so rapidly accumulating in the field of delinquency need to be assembled and reorganized in order to avoid confusion. It is especially desirable to discover a conservative basis for objective diagnosis of deficient intellectual capacity in order to prevent very useful testing systems from becoming unjustly discredited and to preserve the advance that has been made. The work out of which this monograph grew was begun through the encouragement of Judge Edward F. Waite of the Hennepin County Juvenile Court. His earnest co-operation and my interest in the field of mental testing has led me to continue the study. Judge Waite's insight into his court problems resulted in the early organization of a Juvenile Court clinic (_153_, _170_) in Minneapolis. The clinic is in charge of Dr. Harris Dana Newkirk, who has contributed materially to this study by his thorough medical examination of each of the cases brought to him. To the staff at the probation office I am also much indebted. The earnest help of Superintendent D. C. MacKenzie, of the Glen Lake Farm School for the juvenile delinquents of Hennepin County, made a close study of our most interesting group of boys much more profitable personally than I have shown here. For detailed expert work in tabulation and in examinations I wish to express my thanks to my advanced students, a half dozen of whom have contributed materially to the data of this book. JAMES BURT MINER. Carnegie Institute of Technology Pittsburgh, Pa. CHAPTER I. INTRODUCTION