This article focuses on the formation and development of an educational grammar discourse in the age of Enlightenment in 18th century Germany and Russia. The analysis is based on the examples from the German and Russian grammatical works written by J. K. Gotshed, J. K. Adelung and M. V. Lomonosov. Comparative studying of a similar discourse in a diachrony enables to detect similarities and differences, and also the facts of interference and interconditionality. The research revealed the role of individual scientists in formation of an educational grammar discourse, and close connection between scientific and didactic aspects. Furthermore, the analysis of the facts showed that these scientists were familiar with each other's studies. The conducted research also allowed to note similarity between the principles of education developed by these scientists. It is possible to distinguish different branches among these principles, such as education of a general population, role of school, importance of the native language studies, and development of teaching techniques. Beyond that, this article offers the comparative analysis of forewords written by these three authors from the point of view of the target audience and main objectives of these grammatical works. The conclusion of this article indicates the reason behind the importance of studying the 18th century grammatical works.