The article traces the birth of rationalist ideas in the Ukrainian school in the era of early history, namely during the formation of the Kyiv state (X-XI centuries). It is noted that the Byzantine school (IV-VII, and later – X-XII centuries) represented the reception of the classical Hellenic paideia as a unity of content and form and in its main features preserves its functioning in modern educational systems. It is emphasized that the borrowing of the Byzantine model in the field of national education and training was not a simple and unambiguous phenomenon, but a contradictory one, it felt the strong influence of the Slavic pagan culture, which did not know the school as a social institution and did not perceive it as a necessity. The dominant form was home schooling, which met the social needs of the time. The introduction of Christianity as the state religion led to the need for educated people to serve the needs of the state apparatus, which at a certain stage led to the emergence of a school for the systematic organization of education and knowledge transfer. The domestic elite school of the period of the princely era was oriented to the Byzantine educational model, which provided for the introduction of the "seven liberal sciences" (subjects of the trivium and quadrivium) into the Ukrainian education with the introduction into the curriculum of the relevant scientific knowledge that was taught in the educational institutions of the time, which subsequently created a formal basis for the establishment of a rationalist line in Ukrainian education, as a source for the formation and establishment of the ideology of the Enlightenment, the clear manifestation of which is observed in the period of the XVII-XVIII centuries.