Nienhuis Hollow Numerals

Since I had made the children touch the outlines of the geometrical figures in the plane insets, there remained only to make them trace with their fingers the shapes of the letters of the alphabet. (…) At that stage I was struck by an idea which had not entered my mind before: that in writing are employed two different kinds of movement, namely besides the already mentioned movement which reproduces the form there is that of handling the instrument of writing. Indeed, when defective children had become expert in tracing all the letters of the alphabet according to their forms, they were not yet able to hold the pen in their hand. Holding and manipulating a rod with certainty needs a special muscular mechanism which is independent of the movements involved of writing; it is in fact con- temporaneous with the movement necessary for tracing all the letters of the alphabet. It is therefore, a unique mechanism which ought to exist along with the motor memory of the separate graphic signs. There remained the preparation of the muscular mechanism for holding and manipulating the instrument of writing. That I tried to obtain by adding to what had already been described two other exercises. In the first, the letters were touched not only with the index finger of the right hand, as on the first occasion, but with two fingers, the index and the middle finger; in the second, the letters were touched with a wooden rod held like a pen in writing. (…) I thought that, in order to get the movements of writing carried out more exactly, and to guarantee or at least to guide execution on a more direct manner, it would be necessary to prepare hollow letter shapes, so that they were represented by a groove, in which the wooden rod might move.

M. Montessori, The discovery of The Child, Kalakshetra Publications, 1966