The relevance of this study is due to the ever-growing demands that the rapidly developing society makes to the education system, according to which the priority factor in the development of students is the ability to independently plan their activities to acquire the necessary knowledge and skills during joint creative and cognitive activity. It is confirmed that it is during the implementation of projects that it is possible to reveal the potential of students in self-realization, interaction with others and development of critical thinking. The goal of this article is to study the theoretically grounded and practically proven effectiveness of the use of project-based training in the study of mathematics by students of the secondary school. The main method of this research is a pedagogical experiment, as well as observation, a quantitative method and statistical processing. In the process of teaching mathematics, the specifics of project training as a student-centered method aimed at improving analytical and creative skills were taken into account. Gradual methodological methods for the organization of the project activity of students are developed. In the course of testing, model images of lessons were obtained, substantive content was determined and specified, thematic lines of the project activity in teaching mathematics in basic school were built, and the use of variable forms of the project activity was justified. The peculiarities of the author’s approach to the study of the features of project-based learning are the allocation of special criteria for project assessment; comparative analysis of approaches of foreign and domestic scientific schools to the project activity. The study revealed the effectiveness of project-based training in teaching mathematics. The materials of the article are valuable for primary and secondary school teachers, teachers of secondary vocational and higher educational institutions. The use of the project activity in teaching mathematics in basic school contributes to increasing the level of motivation to study the most difficult topics of the course, ensures the implementation of an integrated approach to the study of natural sciences.