The indices for the amount of school retardation are the most significant figures in any of these tables, although they are based on too few numbers to afford more than rough comparisons. It is, however, a fairly reliable estimate to say that retardation in school attainment in Minneapolis is about twice as great among ordinary delinquent boys and among the detention home group while it is three times as great among ordinary delinquent girls as among corresponding groups of elementary school children. If we had been able to credit the groups with those in advance of the expected position for their ages the difference would have been even greater. B. SCHOOL RETARDATIONS AMONG OTHER GROUPS OF DELINQUENTS In view of the fact that retardation in school offers an important check upon the question of the frequency of mental deficiency among groups, besides stating a different training problem of its own, it is curious that it has not been more systematically studied in connection with delinquency. Few investigations include any reference to the question. Auden (_69_) reports that among 263 committed to Borstal institutions (juvenile reformatories) in England for the year ending March 31, 1909, 71% (_186_) had not reached the fourth standard, corresponding to the fourth school grade. These were delinquents between 16 and 21 years of age. The next year 402 out of 554 (72%) had not reached the fourth grade. Not one person had reached the eighth grade and only 13 the seventh grade. In the Minneapolis detention home group only 23 out of the 103 over ten years of age were below the fourth grade. Cornell gives the distribution of 236 boys in special disciplinary classes of two Philadelphia schools (_93_). These classes are for truant and difficult boys 8 to 14 years of age inclusive. While they are not technically delinquents the problem is similar and they show even more serious school retardation than the Minneapolis group. Summarizing his results according to the standard which counts ages six or seven as satisfactory in the first grade, and so on, we find 12.3% satisfactory; 12.3% retarded one year; 26.7% retarded two years; 30.1% retarded three years; 15.8% retarded four years; 2.5% retarded 5 years; and 0.4% retarded 6 years. Eighty-eight per cent. are thus behind a satisfactory position in the grades, and 48.8% three or more years behind. This is to be compared with 70 and 16% among ordinary Minneapolis delinquent boys (Table XIII).