In spite of uncertainty introduced by the use of quotients, the general tendency in interpretation of results with Binet scales has thus been to make a distinction in the amount of retardation signifying deficiency among younger and older children and to require four years retardation, at least for the older ages. Our criterion for the borderline of three years retardation for children under 10 years and four years for 10 years and over, with an extra year to be quite sure that the deficiency is sufficient to justify isolation, seems to be in line with the best practise at present among those who have had much experience with the Binet scale. Fortunately, little harm has been done to the individuals themselves by this uncertainty in the interpretation of the scores with the scale, since only questionable cases have been affected. These have generally been diagnosed, before disposing of the child, by some expert who understands the sources of error in mental tests. On the other hand, shifting the limit of allowable retardation by one year makes a great difference in the estimation of the frequency of feeble-mindedness in particular groups, as will be shown in our discussion of deficient delinquents. ----- Footnote 11: Throughout this study I shall use the literal translation of the German term “lebensalter,” life-age, instead of the awkward “chronological age.” Footnote 12: _S. E._ = √(_p._ _q._/_n_) Footnote 13: Tests XI were recorded as XII in the 1911 series. CHAPTER VI. DELINQUENTS TESTING DEFICIENT A. AT THE GLEN LAKE FARM SCHOOL FOR BOYS, HENNEPIN COUNTY, MINNESOTA. We are now in a position to evaluate the Binet examinations of delinquents. Let us first note our results for a group of 123 consecutive cases at the Hennepin County Detention Home.[14] It is not a detention home in the sense of a place where children are held awaiting the disposition of their cases by the Juvenile Court. It is better described by its unofficial title, The Glen Lake Farm School for Boys. This county training school for delinquents is located on a splendid farm beside a small lake fourteen miles outside of Minneapolis. The boys are sent there by the juvenile court for a few months' training as an intermediate discipline between probation and sentence to the State School at Redwing.