 In 1927, after Vienna’s city council had unified the psychological and pedagogical institutes into a Pedagogic Institute, Popper wrote his first thesis, ‘“Habit” and “Experience of Law” in Education’. There, he justified the scientific status of pedagogy on inductivist grounds. And he raised the fateful philosophical problems of the ‘objective-scientific decidability of pedagogical problems’ and ‘the delimitation of the empirical part of pedagogy from its non-empirical part’ (ter Hark 2002, 88 and Gattei 2004, 454). Selz’s holistic and functional notion of ‘total task’, based on a psychological mechanism of trial and error would inspire Popper’s pedagogy as well as his scientific methodology. Moreover, his awareness of Montessori methods was secured in the 1920s by his teaching education, his friendship with a carpenter who made toys for a Montessori orphanage and turned him to cabinet-making and the Montessori-inspired ‘Socratic method’ of his admired Kantian critical philosopher Leonard Nelson (Hacohen 2000, 90 and 122).