Let us be more precise with regard to two points—the age of the child and his school position. Some heads of schools, not all, have taken the trouble to satisfy our demands, and have fixed to almost a year the mental retardation of the child as compared with normal children of the same age. The following table summarises these replies, and shows that the majority of cases present a retardation of three years:

Mentally defective children with a retardation of—

00
1 year6
2 years12
3 years12
4 years9
5 years0
6 years4
7 years1

According to a convention, of which we shall speak more fully later, we regard as defective in intelligence a child who shows a retardation of three years, when he himself is nine years of age or more. The results shown above agree with this convention. Moreover, one may draw the conclusion, which is of practical value, that one need not seek children of this group in the senior division of a primary school.

The distribution of the ill-balanced in the divisions of the primary school is quite different. In the first place, one is surprised to find none, or practically none (only two out of forty-five) in the senior division. We did not expect this. A priori, we should have supposed that, in spite of their defect in character, the unstable were not without intelligence, and that a fair number of them would succeed in passing the gates of the senior division. If none are found there, this shows clearly that instability must be associated with some mental defect, unless some independent condition, such as inveterate laziness, has checked the child on the way. The ill-balanced, like the simply defective, are to be found in the intermediate and junior divisions, but their distribution is different. While 75 per cent. of the simply defective are in the junior division, and 25 per cent. in the intermediate, 45 per cent. of the ill-balanced are in the junior, and 50 per cent. in the intermediate: practically, they are divided equally between these two divisions. This indicates a degree of intelligence superior to that of the defective, as one would expect. But, on the other hand, their absence from the senior division shows that the intelligence of the ill-balanced is in general below the average. As this conclusion is new, and may be open to question, let us examine it more closely:

The amount of the retardation of the ill-balanced, as shown in our returns, is as follows:

Mentally ill-balanced children with a retardation of—

014
1 year16
2 years14
3 years2
4 years1

These figures show, in a novel form, that the mental retardation is much less clear in the ill-balanced than in the defective properly so called, since in the former group are to be found many pupils—about a third—who, in the opinion of their teachers, are not at all backward; but the majority are backward, while none are in advance of their years. Consequently, the whole group shows a slight retardation, averaging about one year, which confirms and makes more precise our original conclusion. We may therefore affirm that mental instability or want of balance is usually accompanied by an intellectual retardation of about one year.

Age Distribution.—It is worth while making another remark about the ages of these children. The simply defective are of all possible school ages, while the unstable are usually young children. Here is the distribution: