Known affectionately as Mutti by her pupils, Mlle Elsa Hartoch was an integral part of the International School from its founding in 1924 until her death in 1981. Mlle Hartoch was characterized as being the soul of the school by Susan Sweetser in her book One Shining Hour. The daughter of one of the school founders, Arthur Sweetser, Susan was one of the first students in 1924 who remembers Mlle Hartoch as a "fascinating, tenacious teacher who believed in her students."

Mlle. Hartoch, of German origin, had left Russia as a young girl to settle in Geneva where she became an associate of Dr. Adolphe Ferrière, a pioneer in progressive education. Ferrière hosted the International School during its first year at his Geneva chalet, a year in which the new school grew from 8 students to 29. After Ferrière left to establish another school in Lausanne, Mlle Hartoch remained in Geneva to establish new methods of teaching within the Primary School at Ecolint.

Her friendship with the well-known writer and Nobel Laureate Romain Rolland was to become fortuitous for helping Elsa's brother Oskar Oskarovič Gartoch to survive under Stalin's Russia. Oskar Gartoch was a distinguished microbiologist and medical scientist in Leningrad (St. Petersburg) during the 1930s who was subjected to political persecution and arrests for alleged counter-revolutionary activities. At Elsa's request, Romain Rolland interceded on Oskar's behalf with Maxim Gorky in Russia, who was close to Stalin, and succeeded in obtaining Oskar's release.

Upon Gorky's death, Rolland's intercessions were ended and Elsa was prevented from rescuing her brother from subsequent purges. This ultimately led to Gartoch's execution in 1942. His name was later rehabilitated in 1956. This story is recounted in the Russian project: Бессмертный барак (Immortal Barracks) under the tab labeled: "Дополнительная информация (Additional Information)" and also documented by Leipzig University . [Many thanks to Richard Clare for this detailed research.]

Mlle Hartoch remained an important part of the International School throughout her very long life. Stephanie Oats Farrall, Margo Malakoff, Toby James, Rock Brynner, Robin Dormer, Leslie Fernandez Van de Ven, Chris Myers, and pupils across many generations all remember Mutti having enriched so many aspects of school life. Derrick Deane correctly points out that, within Ecolint, Elsa Hartoch has always been referred to as 'Mademoiselle.'

Her pupils have lasting impressions of this remarkable teacher. David Winet, Pierre de Felice, Julie Goodman, Ricky Dassin, and Derrick Deane have shared their fond recollections of Russian language lessons with Mlle Hartoch. Pierre de Felice raconte: " Quand je la revois [sa photo] ainsi je me rappelle les chansons russes qu'elle m'apprenait, aussi chaque fois que j'ecoute Petrouchka de Prokofieff je pense a elle."