This study describes the results of a research that was aimed at studying the dynamics of changes in positive mental states during the educational activities of students at a higher educational institution, their relationship with mental structures and the effectiveness of self-regulation of states. The relationships between mental structures (reflexive, semantic, self-system) and positive mental states were studied and subsequently analyzed during the course of the lesson (the beginning of the lesson, the middle, where the peak of students’ activity is observed, and the end of the lesson). The aim of the study was to analyze the relationship between the structures of consciousness and the effectiveness of self-regulation of positive states in the dynamics of students' educational activities. The study of the characteristics of mental states and the effectiveness of their self-regulation was carried out during the students' performance of a group assignment at a seminar. Separately, outside of educational activities, we diagnosed the severity of mental structures. In our work, we used both well-known questionnaires for diagnosing mental structures and mental states, and specially developed methods for studying the effectiveness of self-regulation and the severity of positive states. As a result, we found that by the middle of the lesson, there is an increase in the activity of experiencing positive states, and by the end, there is a decrease in its intensity. We found that positive states in the classroom are interconnected with the expression of mental structures and a high level of self-regulation efficiency. We found that the effectiveness of self-regulation of states at the beginning of the lesson is associated with semantic structures, in the middle - with value-semantic structures and the self-system, and at the end of the lesson reflexive structures acquire special importance. The results obtained can be used to update and maintain positive states during educational activities and they are novel.