The article discusses the role of the cognitive interest of primary school students as an influential factor that ensures the successful course of educational activities. The article presents the results of an experimental study that revealed a wide range of manifestations of cognitive interests of pupils in grades 2–4 and their influence on learning activity and quality of knowledge. The author describes a diagnostic methodology for studying the breadth, depth, effectiveness, and stability of cognitive interests. The article provides recommendations on the use of integrated and active teaching methods, ensuring continuity between primary and secondary schools, and taking into account the interests of students in planning educational activities. The list of didactic principles, the observance of which ensures the sustainable development of cognitive interests as a driving force of educational activity, is determined. The conclusions show the need for systematic and purposeful formation of cognitive interests in the educational process of primary school.