The cycle's third article considers the Prussian elementary school evolution from the second half of the 19th century to the early 20th century. Special attention is paid to the elementary school system development as well as pedagogical issues of the school organization and management. Scientific and specialized literature on the research topic was used as materials. Methodological basis of the study consisted of the traditional historiography principles historicism, scientific objectivity and consistency. Methods used in the course of work are as follows: comparative method. It allowed comparing the main doctrines of rationalist and canonical Prussian schools. Thanks to the comparative method, it became possible to identify the reasons that allowed German teachers-innovators to seriously advance German pedagogy to the leading positions in the second half of the 19th century. In conclusion, the authors noted that the Reformation and the emerging Protestantism played an important role in the public education system development in Prussia and then in Germany. It was Protestantism that would bring the cause of schooling to a fundamentally new level and create conditions for the German pedagogy establishment. Ultimately, German teachers-innovators would create a rationalist school, which in turn would be focused on the diverse knowledge formation in a student, and this would allow to create a foundation for the entire advanced German science in the future. [For Part 2, see EJ1238495.]