Introduction. The organization of the educational process involves the implementation of ongoing assessment, which provides support for students’ educational activities and the impact on the educational process to improve its effectiveness. One of the elements of the teacher's assessment activity is an assessment judgment, which is formulated by the teacher in the current process of monitoring, diagnosing, analyzing and interpreting the results of students' learning activities and is aimed at informing students about the degree of the planned result achievement, students’ motivation, approval, remark, etc. The study of the teacher's assessment judgments in the context of formative assessment correlates with the problem of reliability, which ensures the consistency, objectivity, fairness and stability of the results of assessment activities.Materials and Methods. The material for the research includes 20 articles published from 2017 to 2020 and devoted to the problems of teachers’ assessment judgments during the process of formative assessment. They were collected by using keywords in the full-text databases of published scientific research which were ScienceDirect and Wiley Online Library. The selected articles were analyzed and summarized from the point of view of considering the factors that influence the teacher's assessment judgments and create conditions for reducing reliability.Results. As a result of the analysis of publications, we identified the following groups of factors that affect the reliability of the teacher's assessment judgments: factors caused by the components of the assessment situation, which include factors related to the subject and object of the assessment, assessment target, scope of the assessment, the basis of the assessment, as well as the use of the assessment tool; factors related to the assessment judgment; external factors.Discussion and Conclusions. The study of the factors influencing the reliability of the teacher's assessment judgments determines the possibilities of increasing the effectiveness of the assessment activities in the process of formative assessment. Understanding the role of each factor creates conditions for preparing recommendations for the teacher to improve the reliability of the current assessment. In addition, on the basis of the classification under consideration, it is possible to conduct empirical studies to clarify the specifics of activating certain factors depending on the goals, conditions and individual characteristics of all participants of the educational process in order to increase the effectiveness of monitoring the achievements of planned educational results and support the educational process.