This article deals with the theory of interests, which, on the basis of data arrived by research, assumes that there are two phases in the development of pupil’s interests: exterior and interior. In the former the pupils are guided by the educational process towards certain activities, in the latter the pupils themselves spontaneously and independently begin to develop the activities to which they have so far been guided. In this phase former exterior interests become interior and this change is connected with the inception of a new quality in the development of interests — the pupil’s own interest with its cognitive, motive and regulating function. The author also stresses the importance of co-operation between school and family for the inception and development of the pupil’s interests.