It had already been noted that little ones of two or three years take the greatest pleasure in arranging small objects, and this experiment in the "Children's Houses" demonstrates the truth of this assertion.

Now, and here is the important point, the normal child attentively observes the relation between the size of the opening and that of the object which he is to place in the mould, and is greatly interested in the game, as is clearly shown by the expression of attention on the little face.

If he mistakes, placing one of the objects in an opening that is small for it, he takes it away, and proceeds to make various trials, seeking the proper opening. If he makes a contrary error, letting the cylinder fall into an opening that is a little too large for it, and then collects all the successive cylinders in openings just a little too large, he will find himself at the last with the big cylinder in his hand while only the smallest opening is empty. The didactic material controls every error. The child proceeds to correct himself, doing this in various ways. Most often he feels the cylinders or shakes them, in order to recognise which are the largest. Sometimes, he sees at a glance where his error lies, pulls the cylinders from the places where they should not be, and puts those left out where they belong, then replaces all the others. The normal child always repeats the exercise with growing interest.

Indeed, it is precisely in these errors that the educational importance of the didactic material lies, and when the child with evident security places each piece in its proper place, he has outgrown the exercise, and this piece of material becomes useless to him.

This self-correction leads the child to concentrate his attention upon the differences of dimensions, and to compare the various pieces. It is in just this comparison that the psycho-sensory exercise lies.

There is, therefore, no question here of teaching the child the knowledge of the dimensions, through the medium of these pieces. Neither is it our aim that the child shall know how to use, without an error, the material presented to him thus performing the exercises well.

That would place our material on the same basis as many others, for example that of Froebel, and would require again the active work of the teacher, who busies herself furnishing knowledge, and making haste to correct every error in order that the child may learn the use of the objects.

Here instead it is the work of the child, the auto-correction, the auto-education which acts, for the teacher must not interfere in the slightest way. No teacher can furnish the child with the agility which he acquires through gymnastic exercises: it is necessary that the pupil perfect himself through his own efforts. It is very much the same with the education of the senses.

It might be said that the same thing is true of every form of education; a man is not what he is because of the teachers he has had, but because of what he has done.

One of the difficulties of putting this method into practice with teachers of the old school, lies in the difficulty of preventing them from intervening when the little child remains for some time puzzled before some error, and with his eyebrows drawn together and his lips puckered, makes repeated efforts to correct himself. When they see this, the old-time teachers are seized with pity, and long, with an almost irresistible force, to help the child. When we prevent this intervention, they burst into words of compassion for the little scholar, but he soon shows in his smiling face the joy of having surmounted an obstacle.