The study examines a new perspective for the use of big data processing technologies that is associated with the possibility of assessing professional competencies of a teacher by means of assessing the learning results of students and contributes to the creation of prerequisites for eliminating professional deficiencies of teachers with the help of new specially designed educational programs. The aim of the study is to develop and test such a technology that makes it possible to analyze the results of assessing procedures of the quality of schoolchildren's education and establish the connection between these results and the level of teachers' professionalism in order to plan further activity to eliminate professional deficiencies and develop teachers' competencies. To implement such a technology, an algorithm has been developed for assessing professionalism and level of teachers' competencies, making possible to assess educational results of students. The technology is based on a cluster approach to data analysis, the methods of clustering k-means and hierarchical clustering have been chosen. In the study, for primary clustering, the learning results of students (Tomsk Oblast) in the national Unified State Exam within the period from 2015 to 2019 were analyzed (subjects: Russian, Mathematics (profile level), Physics, Social Studies). The number of clusters was selected by the selection method, n = 15. The next stage of the study analyzed the results of students within each cluster. The stage made possible to identify groups of “difficult” assignments that 30% or more of schoolchildren could not cope with (subjects: Russian and Mathematics (profile level)). As a result, the assignments that caused the greatest difficulty for schoolchildren were fixed, and thus deficiencies in their knowledge and skills were identified. It was not possible to assess “difficult” assignments in Physics and Social Studies in the framework of the study, since a small number of students had chosen these subjects to pass in the exam. The comparative analysis demonstrated that, within the same cluster, schoolchildren had similar difficulties in doing the same assignments, which that allows us to focus on appropriate teachers' competencies and on subject and methodology deficiencies, and to conduct further activity on assessing the professional competence of teachers focused narrowly. In addition, the study allows us to outline ways of solving the problem of overcoming professional deficits of teachers. Thus, it becomes possible to specifically develop additional professional training programs (advanced/refresher training) for teachers of the same cluster, the curricula of the programs containing topics and learning paths that will improve the educational results of their students, and thereby improve the quality of secondary education in Tomsk Oblast.