Maria Montessori, Gerald Lee Gutek (2004). “The Montessori Method: The Origins of an Educational Innovation : Including an Abridged and Annotated Edition of Maria Montessori's The Montessori Method”, p.116, Rowman & Littlefield
Maria Montessori, Gerald Lee Gutek (2004). “The Montessori Method: The Origins of an Educational Innovation : Including an Abridged and Annotated Edition of Maria Montessori's The Montessori Method”, p.179, Rowman & Littlefield
Maria Montessori (2013). “The Montessori Method: Scientific Pedagogy as Applied to Child Education in the Children's Houses with Additions and Revisions”, p.99, Read Books Ltd