 Montessori's theory and philosophy of education were initially heavily influenced by the work of Jean Marc Gaspard Itard, Édouard Séguin, Friedrich Fröbel, and Johann Heinrich Pestalozzi, all of whom emphasized sensory exploration and manipulatives.Montessori's first work with mentally disabled children, at the Orthophrenic School in 1900–1901, used the methods of Itard and Séguin, training children in physical activities such as walking and the use of a spoon, training their senses by exposure to sights, smells, and tactile experiences, and introducing letters in tactile form.These activities developed into the Montessori "Sensorial" materials.