[1][2][3][4] Studying at home, Knappert received the French secondary education certificate and then obtained a job in a girls boarding school in The Hague.

In her spare time, she followed a religious education course provided by the Vrijzinnige Geloofsgemeenschap NPB (Liberal Community of Faith of the Netherlands Protestant Association).

They pointed her to the work of Thomas Carlyle, John Ruskin and William Morris, critics of industrial society in Victorian era Britain.

She organized a group of 12 middle-class female volunteers who, every week, each received ten girls at home, where they read aloud or talked about serious subjects while making crafts.

In 1894, the efforts of Knappert and Oort led to the establishment of a neighbourhood building in a working class district of Leiden, called Geloof, Hoop, Liefde (Faith, Hope and Love).

In addition to the club for children, young people and even adults, this building hosted drawing and literacy courses, as well as a choir.

During this period, she campaigned for the appointment of factory inspectors, a legal employment contract and shortening of the working day for women.

She developed an impressive number of activities, including the volunteer-led weekly clubs for reading, discussing and craft making.

This led to the establishment of an institution she called Buitenbedrijf, whose aim was to allow working-class youth to spend a week's holiday outdoors.

Between 1916 and 1936 she edited, together with Annie Salomons, a monthly magazine for girls and young women, called Leven en Werken (Living and Working).