Thus, the amount of retardation increases with the years. It is at first two years, then three, then five. But this augmentation in the amount of retardation, which is the first fact to strike the attention, ought not to conceal from us that there is real progress in the mental condition and in the studies; in fact, we may remark that if a defective child, in passing from the age of eight to eleven, has an augmentation of retardation of one year with respect to his companions, this proves that in the same time he has progressed two years with respect to himself. It is like an omnibus which goes more and more slowly, yet advances all the same. To be more precise, let us say that, since the defectives reach, as an upper limit, the intermediate course, and that in the proportion of two-thirds, one may conclude that they make nearly half the progress of the normal children. Be it understood, this is only roughly true, and many reservations must be made with regard to details. But the indication which these documents afford is, nevertheless, very instructive, for it shows us that the majority, two-thirds at least, of the defectives appear regularly to duplicate each class, or to take two years to pass a stage which the normal child passes in one. It is important to remember this, for the teachers do not always give the facts their true value. They have a tendency to compare the slow progress of the defective with the more rapid progress of the normal, and to conclude from this comparison that the defective remains stationary. This is a pure illusion, which may be compared to what one experiences when looking out of the window of a train in motion. One sees another train going in the same direction but more slowly, and imagines that the second train is not moving. Let us retain, therefore, provisionally, the following important idea: _Only half the defectives in an ordinary school reach with difficulty the intermediate course, first year, passing through the different stages in double the normal time._ No doubt one would find many examples of slower progress still, three or four times the normal. On the other hand, the teacher sometimes points out a defective who has improved very rapidly, as if his intellect awoke from a long sleep. Such cases exist, but they are very rare, and they are open to the suspicion that an error in diagnosis has been made, and that the child who has improved so greatly was wrongly considered defective. With regard to the ill-balanced, the success of the ordinary school is much greater. A recent inquiry taught us that in the course of two years half the children noted as ill-balanced were regarded by the teachers as improved. This figure speaks for itself.