In the years 1900-1915 he was an active member of the Summer Camp Society (later he collaborated with the Polish Culture Society and the Warsaw Hygiene Society amongst others). In the final years of his medical studies, he began to work at holiday camps: in 1904 and 1907 he worked as a tutor of Jewish children at summer holiday centres. These experiences were the basis for the following pedagogical work and resulted in two books: Mośki, Joski, Srule (published in 1910) and Józki, Jaśki i Franki (published in 1911).
In March 1905 Henryk Goldszmit obtained his PhD and began working at the Jewish Berson and Bauman Hospital for Children in Śliska 51 street in Warsaw. As the resident doctor, he was obliged to provide 24-hour care to the ill and medical advice in the hospital's infirmary (regardless of faith); apart from that he also acted as a home-visiting doctor. Korczak was drafted to the Russian-Japanese war and in the years 1905-1906 gained experience as a military doctor.
In order to deepen his medical knowledge, he went to Berlin for a year (1907/1908) and Paris for half a year (1910). There he attended lectures on paediatrics and pedagogy. He took the opportunity to observe children's hospitals and centres providing therapy and education to the youngest. In 1910 or 1911 he stayed in London for a month, where he visited the local schools and nursing homes. It is there, where he decided not to have a family of his own and to devote his life solely to work with children.
Orphans Society
In 1912 he once and for all gave up work at the hospital and took up the post of director of the newly-opened Jewish House of Orphans, which operated under the patronage of the Help to the Orphans Society. There he collaborated with Stefania Wilczyńska, who helped him implement his authorial pedagogical concepts and creatively contributed to the development of the establishment. The House of Orphans became for Korczak a place of daily detailed observation of the psychophysical development of a child. There, innovative pedagogical ideas were conceived, such as that of the children's parliament, court, newspaper and notary.