Two of the greatest Dutch educationalists of the twentieth century, Philipp Abraham Kohnstamm (1875-1951) and Martinus Jan Langeveld (1905-1989), believed that education meant, above all, the formation of a conscience. They developed their ideas in a time full of developments within Europe: the rise of fascism, two world wars, and pioneering theories on human development by Charles Darwin (1809-1882) and Sigmund Freud (1856-1939), among others. Kohnstamm's and Langeveld's educational theories were also influenced, to a greater or lesser extent, by optimistic ideas about the spontaneous development of the child and the unique personality of humankind, as expressed in movements such as New Education, New Psychology, and the philosophy of Henri Bergson (1859-1941). This article aims to compare these two Dutch educationalists on conscience formation to contextualise their differences and similarities and subsequently understand them within European developments, such as New Psychology, and specifically the Dutch context of the twentieth century.