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.114, Rowman & Littlefield
David Rakoff (2005). “Don't Get Too Comfortable: The Indignities of Coach Class, The Torments of Low Thread Count, The Never- Ending Quest for Artisanal Olive Oil, and Other First World Problems”, p.76, Anchor