Such doubts, which are known to all investigators, led us to decide to make direct observations on our own account upon abnormal school-children, and to compare them with normal children of the same age--a long and difficult task, as all pioneer work is. We have collected facts which we were not seeking, whilst we often failed to find what we expected. It would be impossible to summarise here everything which contact with reality has taught and suggested. We shall extract from our observations only what concerns the aptitudes of the abnormal, and shall even limit ourselves to a single category of these. It happens that we have methodical observations relating to twelve defective children of between eleven and twelve years of age. These form a sufficiently homogeneous group from the point of view both of age and of mental ability. We shall inquire what are the best marked aptitudes and the most apparent deficiencies of this little group. Without denying individual differences or forgetting that defectives cannot easily be reduced to a single type, we have thought it more interesting for the present to emphasise their resemblances rather than their differences. Let us, then, compare them _en bloc_ with a group of normal children of the same age and the same social position, attending the same schools, in the same district. This equivalence of conditions is necessary if we are to lay our finger on the distinctive characters of the defective child. We have subjected our twelve defectives to certain tests as speedy and precise as possible.[3] We devised these tests before studying the returns furnished to our questionnaires, and the latter were tabulated before our observations. There have, therefore, been two studies absolutely independent, both in their mode of execution, and in their aim. Consequently, any points in which they agree will be very significant. Our collection of tests of mental deficiency is already known to readers of the _Année Psychologique_.[4] In vol. xi. we described at length the details necessary for making use of our method of experimentation. Since then Dr. Decroly, who specialises on defective children in Belgium, has tried our methods, and verified our conclusions. The end which we have constantly set before ourselves has been to bring to light the intellectual capacity of the child, taken by itself, as distinct from what the child actually knows. Our psychological examinations are consequently the very opposite of school examinations, which test chiefly the candidate's memory, his judgment very little. We have made numerous observations in this way. The best way to explain our method, and more especially our results, will be to describe a few of the experiments. _Memory of Pictures of Known Objects._--The children are allowed to look for thirty seconds at pictures of thirteen objects, which they are then told to enumerate from memory.