T. IMSS (Trends in International Mathematics and Science Study) is a program for assessing students’ mastery of mathematics and natural sciences.  It allows us to determine and compare the level and quality of teaching mathematics and natural sciences of high school students in different countries of the world, as well as the changes taking place in the national education system.  It is carried out in a consortium of leading international scientific organizations with the participation of national centers by the International Association for the Evaluation of Educational Achievements.  The international coordinating research center is Boston College (International Study Center, Boston College, USA).  The study has been conducted since 1995 in four-year cycles and is one of the most prestigious international studies in the field of secondary education.  The number of countries covered by the research program is gradually increasing.  The purpose of this study is to compare the readiness of 4th and 8th-grade students in mathematics and natural sciences in countries with different educational systems, as well as to determine the characteristics of educational systems that determine different levels of student achievement.  The research is conducted once in four years.  The seventh cycle of research was conducted in 2019. Previous research was conducted in 1995, 1999, 2003, 2007, 2011 and 2015.  More than 60 countries participated in the 2019 TIMSS survey.
 The purpose of the study is to compare the general educational preparation of high school students in mathematics and natural sciences in countries with different educational systems and to determine the factors affecting the level of this educational preparation.  Research shows that its results make it possible to observe the traditions of education in mathematics and natural sciences when 4th graders become 8th graders every four years. In addition, the specific characteristics of the content and educational process of mathematics and natural sciences education in the participating countries, as well as factors related to the characteristics of educational institutions, teachers, students, and their families are studied. The methodological basis of the research is a conceptual model of evaluating the educational achievements of students, which allows for analysis of the correlation between the level of planned and implemented education on the one hand, and the level of education achieved (educational results) on the other hand.  Within this model, education is considered from three levels of situation:
* The planned level is a social order in an educational institution.  At the planned level, formal goals of education and a set of pedagogical and methodological ideas collected in society are formed, which are reflected in curricula and training manuals.
* The degree to be implemented is the actual educational process of the educational institution.  At the implementation level, the teacher of the educational institution forms the planned content of education in the real (real) educational process.
* The level achieved is the result of education in an educational institution.  Educational achievements, knowledge, skills, and attitudes of students are evaluated at the achieved level.