The selection of the children for the experiment was effected in the following manner. The teachers at Public School 64 were asked to report any cases which had come to their notice, as being seriously afflicted with adenoids and diseased tonsils. In this way a fairly large group was obtained. The parents of the children were visited with the purpose of obtaining permission for examination and operation at the Post Graduate Hospital. It was fairly easy to obtain permission to have the children examined. They were taken in groups of four or five to the clinic, the experimenter attending in person every examination in order to learn from the doctors the degree of the defect. As a result of this method, we discarded all those cases where there was any doubt as to the serious nature of the defect. From the large group examined, we were finally successful in securing operative treatment for 10 children. Discarding the cases where defect was slight, there remained a number of children who, for one reason or another, did not undergo operation. In some instances the parents refused their permission, in some they failed to keep appointments, in one or two there was sickness in the family, and in a number the hospital was overcrowded and could not receive the children. All members of this group were examined,--to the number of fifty-six, and from them the control group was finally selected. Since we were unable to secure a large test group from Public School 64, the experiment was continued at the Manhattan Eye, Ear and Throat Hospital where opportunity was given for testing the children after they had been admitted for operation. In order to be sure that in each case the defect was sufficiently pronounced to render decisive the results of the experiment, each child's card was examined. Only those children were included who were undergoing operation for both adenoids and tonsils. It may be here remarked that mental tests were given to these children on the morning of operation, and in some cases only a short time before it. The possibility suggests itself, therefore, that the results of the tests may have been influenced by excitement or fright on the part of the patients. Actually, however, this did not seem to be the case. The children were perfectly cheerful and showed no signs of nervousness. The tests were given in a waiting room with the door closed so that any disturbing sights and sounds were eliminated. The possible lowering of the performance by the causes mentioned would tend to exaggerate the improvement shown by the retests, so that in the light of the results, it will be seen that they could have had little effect.