In the last few decades, student achievement has played a central role among the indicators used to evaluate the quality of education systems. Accordingly, education reform in Slovenia from the mid 1990s included the achievement of international standards of knowledge and skills as an important goal. In order to provide additional information for the purposes of evaluating the quality of mathematics education in Slovenia, the present study examines mathematics achievement of students in the final grade of the non-reformed compulsory education in Slovenia in an international context. Data from the Third International Mathematics and Science Study (TIMSS) were used to provide information about this achievement in comparison with the achievements of students from other European countries, which are taken as a point of reference for evaluating the achievement of Slovene students. Another point of reference is derived from the attainment targets in the reformed mathematics curriculum. The goal of the study was to provide supporting information for successful implementation of the reforms.