Abadie, for example, has expressly noted that in some schools the proportion may be four times as great as in others. (2) The definition of a child of backward intelligence has usually and quite gratuitously been left vague by the investigators; each interprets the term in his own way, whence arise great differences in the figures. (3) It is particularly difficult to define the cases that are to be reckoned as ill-balanced or unstable, and some teachers, if they are allowed, will place in this category all the pupils that they dislike. * * * * * We have been led to interest ourselves in abnormal children in the following way: One of us, Binet, President of the _Société Libre pour l'Étude de l'Enfant_, has for many years been in daily contact with the staff of the primary schools. In obedience to the wish of a great many teachers, he has formed, in connection with the Society, a committee for the care of abnormal children, upon which are many distinguished people, such as M. Rollet, M. Albanel, Dr. Voisin, Mme. Meusy, and, above all, M. Baguer, who is deeply interested in the education of defectives. This committee initiated various investigations relating to backward children. Some time afterwards M. Binet, having been nominated a member of the Ministerial Commission on Abnormal Children, became the director of the work of the Commission relating to the backward and the unstable. He then, in conjunction with Dr. Simon, undertook in certain districts various inquiries into the condition of such cases. In regard to several questions we enjoyed the intelligent and devoted co-operation of M. Vaney, Head of the Primary School of the Rue Grange-aux-Belles, where one of us has founded a laboratory of pedagogy. We have thus been interested in abnormal children for a long time, either from the point of view of school organisation, or from that of their differentiation from the normal. Let us add that lately M. Bédorez, the distinguished Director of Primary Education in the Seine District, has kindly permitted one of us (Binet) to co-operate in the organisation of some classes for defective children, which have been started experimentally in the primary schools of Paris.