Montessori called the usual disciplines of knowledge the psychodisciplines to convey the idea that the study of the disciplines is not purely intellectual but also affects the learner’s psyche and the disciplines should be studied as interrelated systems providing a view of the interdependence of all knowledge and human attainments. (Boehnlein, Kahn)

In her preface to Psychoarithmetic Maria Montessori states the book “is outside the traditional convention of elementary school teaching and place(s) the psychic development of the child above academic discipline.” (p. xix) “Arithmetic, as presented in this book, contains a heretofore unpublished component of ‘child psychology’, in which the position is taken that arithmetic is a form of reasoning, and the child is a reasoning being. Numbers, along with its derivatives, are scientific stimuli that bring about psychic activity.” (p. xviii) In Psychogeometry she states “In fact, learning is subject to an essential condition; that the pupil agrees to receive the knowledge, and is able to pay attention or, in other words, is interested. His psychic activity is the sine qua non for success.” (p. 4)