=A retardation of three years indicates a child who should be regarded as a suspect.= A child enters the elementary school at the age of about six years. Each year he ought to advance one class. From six to nine years he is in the elementary course; from nine to eleven in the intermediate course; from eleven to thirteen in the senior course. All are not quite regular. Some are a little in advance, some are behind, but the majority conform to the preceding scheme. When a school is well managed, when the assignation of the children to their respective classes is made by means of suitable tests, and without too great regard to the demands of the parents, the classification which results is very good. There is then no better means of finding out whether a child is intelligent or not than to take into consideration his age and his class. Intelligence, so extraordinarily difficult to judge, is indicated in the above way with a really curious exactness. A child two years behind his age, when irregularities in attendance, absence on account of illness, etc., do not explain his backwardness, is very likely to be less intelligent than one who is in, or in advance of, the usual class for his age. This amounts to judging intelligence by the degree of instruction. Theoretically, such a method is open to plenty of meticulous objections, of which the most important is that we are confounding intelligence and memory. To this we shall reply that the stage of instruction reached is not the result of memory alone. It presupposes also some degree of application, some facility of comprehension, quite a collection of diverse aptitudes. The child's success in his studies is, in fact, the best indication we have of his capacity to adapt himself to the school environment. If the child is unable to keep up with the classes suited to his age, if he is unable to profit like other children from the education provided, this shows that he has not the same degree or the same kind of intelligence as his companions, and there is a presumption, if not an absolute demonstration, that his intelligence is inferior to the average, or that his character is different. From these statements, which we have expounded at length elsewhere,[6] it follows that not only the head-master, but an entire stranger, can determine which are the less intelligent children, the less well adapted to that school, without taking the trouble to interrogate them all individually. It is only necessary to compare their position in school with their age.