A significant turning point came in 1844 when he took over the private boys' educational institution established by the late Ernst August Heinrich Heimburg.
In the same year, he established a pedagogical seminary with an attached elementary school, effectively merging theoretical and practical teacher training.
Stoy's reputation as an educator reached new heights in 1865 when he was called upon to fill the newly created chair of pedagogy at the University of Heidelberg.
In 1867, he took a temporary leave of absence to establish an evangelical teacher's seminary in Bielitz, located in the Austrian part of Silesia.
He left behind a remarkable legacy, having dedicated his life to advancing the field of education and shaping the minds of countless individuals.